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Full text of "Philosophical transactions of the Royal Society of London"

THE ROYAL SOCIETY. 



30th November, 1895, 






THE EOTAL SOCIETY. Nov. 30, 1895. 



Her Sacred Majesty QUEEN VICTORIA, Patron. 



Date of Election. 

1863. Feb. 12. 
1882. Mar. 16. 
1893. June 8. 



HIS ROYAL HIGHNESS THE PRINCE OF WALES, K.G. 
HIS ROYAL HIGHNESS TEE DUKE OF EDINBURGH, K.G. 
HIS ROYAL HIGHNESS THE DUKE OF YORK, K.G. 



THE COUNCIL 



01.' 



THE EOYAL SOOIETI 



SIR JOSEPH LISTER, Bart., F.R.C.S, D.C.L.— President. 



SIR JOHN EVANS, K.C.B., D.C.L., LL.D.— 

Teeasfjeee and Vice-Peesident. 
PROF. MICHAEL FOSTER, M.A.. M.D.— 

Seceetaet. 
THE LORD RATLEIGH, MA., D.C.L.— Secee- 

TAET. 

EDWARD FRANKLAND, D.C.L., LL.D.— 

Foreign Seceetaet. 
WILLIAM CROOKES, F.O.S.— Vice-President. 
SIR JOSEPH FAYRER, K.C.S.I. 
LAZARUS FLETCHER, MA. 
WALTER HOLBROOK GASKELL, M.D. 
WILLIAM HUGGINS, D.C.L.— Vice-President. 
THE LORD KELVIN, D.C.L. 



PROF. ALEXANDER B. W. KENNEDY, 

LL.D. 
PROF. HORACE LAMB, MA. 
PROF. EDWIN RAT LANKESTER, MA.— 

Vice-President. 
PROF. CHARLES LAPWORTH, LL.D. 
MAJOR PERCY ALEXANDER MacMAHON, 

fi.A. 
PROF. JOHN HENRY POYNTING, D.Sc. 
PROF. ARTHUR WILLIAM RUCKER, MA. 
OS BERT SALVIN, MA. 
PROF. HARRY MARSHALL WARD, D.Sc. 
ADML. WILLIAM JAMES LLOYD WHARTON, 

C.B. 



This Council will continue till November 30, 1896. 



Assistant-Secretary and Librarian. 
HERBERT RIX, B.A. 



Clerk. 

THEODORE E. JAMES. 



Assistant Librarian. 
A. HASTINGS WHITE. 



Office and, Library Assistant. 
RICHARD CHAPMAN. 



Omissions having occasionally occurred in the Annual List of Deceased Fellows, as announced from the 
Chair at the Anniversary Meeting of the Royal Society, it is requested that any information on that subject, as 
also Notice of Changes of Residence, be addressed to the Assistant Secretary. 



FELLOWS OF THE SOCIETY. 

NOVEMBER 30, 1895. 



(C) prefixed to a name indicates the award of the Copley Medal. 

(E) Royal Medal. 

(Em) Eumford Medal. 

(D) Davy Medal. 

(D\v.) Darwin Medal. 

(t) . . . . is liable to an annual payment of £4. 

{*) £3. 



Date of Election. 

June ~7, 1860. 



June 1, 1876 



Jan. 21, 1847 



June 6, 1872. 



June 7, 1883. 



June 6, 1889 
June 3, 1880 

June 1, 1854 



June 12, 1884. 



June 12, 1879. 



June 4, 1891 



Served on 
Council. 

'67-69 
'77-79 



"83-85 
'91-93 



'58-59 



'82-84 



R. 



'71-73 



Rm, 



R. 



f Abel, Sir Frederick Augustus, Bart., K.C.B. D.C.L. (Oxon.) D.Sc, (Camb.) V.P.C.S. 
Y.P.S. Arts. Hon. Mem. Inst. C.E., Inst. M.E., Ord. Imp. Bras. Rosae Eq. 
Hon. Mem. Deutsch. Chem. Gesell., Mem. Soc. d'Encourag. Paris, Sec. and 
Director of the Imperial Institute. 2 Whitehall-court, S.W.; and Imperial 
Institute, Imperial Institute-road. S.W. 

Abney, William de Wiveleslie, Capt. R.E. C.B. D.C.L. (Dunelm.) F.I.C. F.C.S. 
F.R.A.S., Director for Science in the Science and Art Department. Rathmore 
Lodge, Bolton-gardens South, Earl's Court, S.W. ; and Athenaeum Club. S.W. 

Acland, Sir Henry Wentworth Dyke, Bart., K.C.B. A.M. M.D. LL.D. (Cantab.) 
F.R.G.S., Coll. Reg. Med. Soc, Hon. Student of Ch. Ch., Radcliffe Librarian 
and late Reg. Prof, of Medicine in the University of Oxford. Broad-street, 
Oxford. 

Adams, William Grylls, M.A. D.Sc. F.G.S. F.C.P.S. Vice-President of Physical 
Soc. Past Pres. Inst. Elec. Eng. Professor of Natural Philosophy and 
Astronomy in King's College, London. 43 Campden-hill-square. W. 

* Aitchison, James Edw. Tierney, M.D. CLE., LL.D. (Edin.) F.R.S.E. F.L.S. 

F.R.C.S. (Edin.) M.R.C.P. (Edin.) Corresp. Fell. Obstet. Soc. Edin. Brigade 
Surgeon H.M. Bengal Army (retired). 20 Chester-street, Edinburgh. 

* Aitken, John, F.R.S.E. Darroch, Falkirk. N.B. 

* Allbutt, Thomas Clifford, M.A. M.D. LL.D. F.L.S. Regius Professor of Physic in 

the University of Cambridge. St. RadeguiuTs, Cambridge. 
Allman, George James, M.D. LL.D. F.R.S.E. F.R.C.S.I. F.L.S. M.R.I.A. Cor. 
Mem. Z.S. Emeritus Regius Professor of Natural History in the University of 
Edinburgh, Ex-Pres. of the Linnean Society, Hon. Fell. Roy. Micros. Soc, 
Hon. Mem. Geol. Soc. Cornwall, Phil. Soc. Yorkshire, Lit. Antiq. Soc. Perth, 
Trin. Hist. Soc. Dallas, Texas, Soc. Reg.Sci.Dan.Hafn.Soc.Honor. Soc. Zool. 
Bot. Vindob. Socius Honor. Soc. Hist. Nat. Ind. Batav. Corr. Ardmorc, 
Paristone, Poole, Dorsetshire ; and Athenceum Club. S.W. 

* Allman, George Johnston, LL.D. (Dubl.) D.Sc. Emeritus Professor of Mathe- 

matics in Queen's College, Galway, Member of Senate of the Royal Uni- 
versity of Ireland. St. Mary's, Galway. 
Anderson. John, M.D. LL.D. (Edin.) F.R.S.E. F.S.A. F.L.S. F.Z.S. late Superin- 
tendent, Indian Museum, and Professor of Comparative. Anatomy in the 
Medical College. Calcutta. 71 Harrington-gardens. S.W. 

* Anderson, William, D.C.L. Past Pres. Inst. Mech.E., Mem. Inst. C.E., Director- 

General of Royal Ordnance Factories. Lesney House, Erith ; and Royal 
Arsenal, Woolwich. 



(5 

Date of Election. 

June 7, 1888 
June 3, 1875 
June 19, 1851. 

June 12, 1878. 
June 1, 1876. 
May 7, 1846. 



Jane 3, 1880, 



June 2, 1881. 

June 4, 1885 
June 5. 18'.K). 

June 6, 1878 
Jan. 12, 1888 
June 12, 1884. 



Served on 
Council. 



'55-5(5 
'83-84 



'88-90 



'ol-6>i 



'89- 9 L 



'92-93 



'83-84 



'92-94 



FELLOWS OF THE SOCIETY. (Nov. 30, 1895.) 

* Andrews, Thomas, F.R.S.E. F.C.S.Mem. Inst. C.E., Telford Medallist and Prize- 
man. Havencrag, Worthy, near Sheffield. 

Archer, William, M.R.I.A. National Library of Ireland; and 52 Lower Mount- 
street, Dublin. 

f Argyll, George Douglas Campbell, Duke of, K.G. K.T. D.C.L. (Oxon.) LL.D. 
(Camb.) Trust. Brit. Mus. Hon. V.P.R.S. Edin. F.G.S. Argyll Lodge, Ken- 
sington, W. ; and Inverary Castle, Argyleskire. 

f Armstrong, Sir Alexander, K.C.B. M.D. LL.D. (Dubl.) F.R.G.S. late Director- 
General of the Medical Department of the Navy, Hon. Physician to the 
Queen and to H.R.H. The Prince of Wales. The Elms, Sutton Bonnington, 
Loughborough, Leicester shire. 

\ Armstrong, Henry Edward, Ph.D. (Lips.) LL.D. (St. Andr.) Pres. Chern. Soc. 
Professor of Chemistry at the City and Guilds of London Central Institute, 
South Kensington, Hon. Mem. Pharm. Soc. Loud. 55 Granville-parh, 
Lewisham. S.E. 
Armstrong, William George, Lord, C.B. D.C.L. (Oxon.) LL.D. (Cantab.) M.E. 
(Dubl.) Ord.SS™ m - Maur. et Lazar. Ital. Gr. Off. Ord. Dannebrog et Ord. 
Jes. Christ Portog. Com. Ord. Fr. Jos. Austriae, Ord. Car. III. Hisp. et Ord. 
Imp. Bras. Rosae Eq. Athenaum Club; Cragside, Rothbury ; and Newcastle- 
upon-Tyne. 

* Attfield, John, M.A. Ph.D. (Tub.) F.I.C. F.C.S. Professor of Practical Chemistry 
to the Pharmaceutical Society of Great Britain, Hon. Mem. Amer, Pharm. 
Assoc, Colls. Pharm. Philad., New York, Mass., Chic, Ontario, and Pharm. 
Assocs. Liverp., Manch., Maryland, Virg., Georgia, New Hampshire, and 
Quebec, Hon. Corresp, Mem. Soc. Pharm. Paris, Hon. Mem. Pharm. Soc. 
Gr, Brit., New South Wales, St. Petersb., Austria, Denmark, East Flanders, 
Switzerland, Queensland, and Australasia. Ashlands, Watford; and 17 
Bloomsbury-sq. W.C. 

* Ayrton, William Edward, Mem. Phys. Soc. and Inst. Elect. Eng., Professor of 
Apphed Physics in the Guilds Central Technical College. Exhibition-road. 
S.W. 

* Baird, Andrew Wilson, Lieut.-Colonel, R.E. Care of Messrs. Grindlay, Groom $ Co., 
Bombay, India. 

Baker, Sir Benjamin, K.C.M.G. LL.D. M.E. (Dubl.) Mem. Inst. C.E., Hon. 

Mem. Amer. Soc. Mechan. Engs., Soc of Engs., and Mane. Lit. and Phil. 

Soc. 2 Queen-square-plaee, Queen Amies Mansions, Westminster ; and 

Athenwum Club. S.W. 
I" Baker, John Gilbert, F.L.S. Keeper of the Herbarium, Royal Gardens, Kew. 

Royal Herbarium, Kew. 
t Balfour, Right Hon. Arthur James, D.C.L. 4 Carlton- gardens, S.W. ; and 

Wlnttinghame, Prestonkirk, N.B. 

* Balfour, Isaac Bayley, D.Sc. M.D. (Edin.) M.A. (Oxon.) F.R.S.E. F.L.S. F.G.S. 
Keeper of the Royal Botanic Garden, Edinburgh, Queen's Botanist in 
Scotland, and Professor of Botany in the University of Edinburgh, 
Corresp. Mem. Deutsch. Bot. Gesell., Soc. Nat. des Sci. Nat. et Math. 



Cherbourg. 



In cerfeith House, Edinburgh ; and Athenaum Club. S.W. 



Date of Election. 

June 5BT 1873 



June 6, 1889 
June 2, 1864. 

June 6, 1850. 

Dec. 12,1844. 
June 13, 1895. 
June 6, 1889. 
June 4, 1868. 



Feb. 8, 1838 
June 7,1891 

June 11, 1857 



Served on 
Council. 



'80-81 



'65-67 



June 2, 1892 



June 12. 1873. 



June 4, 1874 

June 12, 1884 

June 8, 1871. 

June 12, 1879. 
June 4, 1886, 
April 6, 1843, 
June 4,1874, 



'81-82 



'91-93 



FELLOWS OF THE SOCIETY. (Nov. 30, 1895.) 7 

Ball, Sir Robert Stawell, Kt., Hon. M.A. (Cantab.) LL.D. M.R.I.A. Soc. Phil. 
Cam. et Soc. Reg. Edin. Soc. Honor. Lowndean Professor of Astronomy 
and Geometry in the University of Cambridge. The Observatory, 
Cambridge; and Athenwum Club, S. W. 

* Ballard, Edward, M.D. 6 Ravenscroft-park, High Barnet, Herts. 

t Barkly, Sir Henry. G.C.M.G. K.C.B. F.R.G-.S. 1 Bina-gardens, South Kensington, 
S.W. 
Barlow, William Henry, F.R.S.E. Past Pres. Inst. C.E. High Combe, Old 

Charlton, Kent. 
Barrow, John, F.S.A., F.R.G-.S. 17 Hanover-terrace, Regent's Park. N.W. 

* Barry, John Wolfe, C.B. V.P. Inst. C.E. 23 Delahay-street, Westminster. S.W. 

* Basset, Alfred Barnard, M.A. Fledborough Hall, Holyport, Berks. 
Bastian, Henry Charlton, M.A. M.D. F.L.S. Coll. Reg. Med. Soc. Professor of 

the Principles and Practice of Medicine, University College, Physician 
to University College Hospital, Fellow of Univ. Coll. London, Hon. Fellow 
Roy. Coll. Phys., Ireland, Corr. Mem. Roy. Acad. Med. Turin and Soc. 
Psychol. Physiolog. Paris. 8a Manchester-square. W. 
f Baternan. James, M.A. F.L.S. Home House, Worthing. 

Bateson, William, M.A., Fellow of St. John's College, Cambridge. St. Johns 
College, Cambiidge. 

Beale, Lionel Smith, M.B. Coll. Reg. Med. Socius. Prof, of the Principles and Practice 
of Medicine, and formerly of Physiology and of General and Morbid 
Anatomy, and of Pathological Anatomy in King's College, London, and 
Physician to the Hospital. Government Medical Referee for England. 61 
Grosvenor-street. W. 

* Beddard, Frank Evers, M.A. (Oxon.), F.R.S.E., F.Z.S., Lecturer on Comparative 

Anatomy, Guy's Hospital, Prosector to the Zoological Society. Zoological 

Society's Gardens, Regent's Park. N.W. 
f Beddoe, John. M.D. LL.D. (Edin.) B.A., Officier de l'lnstr. Publ. France ; Vice- 

Pres. Anthrop. Inst. Corresp. Mem. Anthrop. Soc. Berlin, Soc. Romana 

di Antrop. ; For. Mem. Soc. Anthrop. Paris ; Hon. Mem. Anthrop. Socs. 

Brussels and Washington, Acad. Anthrop. New York, Arner. Antiq. Soc. 

and of Imp. Soc. Friends of Sci., Moscow. The Chantry , Br adford-on-Avon ; 

and Ailienceum Club. S.W. 
t Bell, Sir Lowthian. Bart., F.C.S. Mem. Inst. C.E. Roimton Grange, by 

Northallerton. 

* Bell, James, C.B. D.Sc. (Dubl.) Ph.D. F.I.C. Late Principal of the Inland Revenue 

Laboratory, Somerset House. Hoxoell Plill Lodge, Eioet'l, Surrey. 
Besant, William Henry, D.Sc. F.R.A.S. Fellow of St. John';; College, Cambridge. 
St. Johns College, and Spring fjavm., Harvey-road, Cambridge. 

* Bessemer, Sir Henry, Hon. Mem. Inst. C.E. Denmark-hill. S.E. 

* Bidwell, Shelford, M.A.LL.B. Riverstone Lodge, Southjields, Wandsworth S.W. 
Blake, Henry Wollaston, M.A. 8 Devonshire-place, Portland place. W. 

t Blanford, William Thomas, LL.D. (Univ. McGill) A.R.S.M. F.G.S. F.R.G.S. 
F.Z.S. Ord. SS™- Maur. et Lazar. Ital. Eq. Soc. Asiat. Beng. Soc. Honor. 
72 Bedford-gardens, Campden-hill, Kensington. W. 



8 

Date of Election. 

June 6, 1878, 



Served on 
Council, 

'80-82 
• '95 



June 5, 1890 
June 7, 1888. 
June 7, 1894 
June 13, 1895. 
June 4. 1891. 



June 3, 1858 
June 7, 1888. 



June 7, 1894. 
June 8, 1882. 

June 12, 1873. '77-7 



June 3, 1875. 
Juue 12, 1879 



June 6, 1889 
June 7, 1883 

June 4, 1874. 

June 13, 1895. 

Dec. 14, 1893 
June 9, 1887 

June 1, 1866. 



'91-92 



'82-84 



F.C.S. Lecturer on 
13 University-gardens, 



FELLOWS OF THE SOCIETY. (Nov. 30, 1895.) 

Bonney, Rev. Thomas George, D.Sc. LL.D. (Univ. McGill) Sc.D. (Dubl.) F.S.A. 
F.G.S. Soc. Phil. Cantab. Soc. et Ebor. Soc. Honor. Soc. Geol. Belg. et 
Soc. Reg. Canad. Corresp. Corresp. Mem. Soc. Geol. du Nord de France, 
Professor of Geology in University College, London. 23 Denning-road, 
Hampstcad. N.W. 

* Bosanquet, Robert Holford Macdowall, M.A. Fellow of St. John's College, 

Oxford. Castillo Zamora, Realejo-Alto, Teneriffe; and New University 
Club, St. James' s-street. S.W. 

* Bottomley. James Thomson, M.A. D.Sc. F.R.S.E. 

Natural Philosophy hi the University of Glasgow. 
Glasgow. 

* Boulenger, George Albert, F.Z.S. Corresp. Mem. Imp. Soc. Friends of Sci., 
Moscow, Senckenb. Soc. Frankfort, Linn. Soc. Bordeaux, Sci. Soc. Boston. 
8 Courtfieid-road, South Kensington. S.W. 

* Boiu-ne, Alfred Gibbs, D.Sc. Professor of Biology in the Presidency College, 
Madras. Fellow of University College, London. Presidency College, 
Madras. 

Bower, Frederick Orpeu, D.Sc. (Camb.) F.L.S. F.R.S.E. Regius Professor of 
Botany in the University of Glasgow. 45 Kerrsland-terrace, Hillhead, 
Glasgow. 
f Boxer, Edward Mounier, Major-General, R.A. Upton, near Ryde. 

* Boys, Charles Vernon, A. R.S.M. Assistant Professor of Physics in the Royal College 
of Science, London, Officier de l'lnstruction Publique, France. Royal College 
of Science, South Kensington ; and Glebe House, Glebe Place, Chelsea. S.W. 

Bradford, John Rose, M.D. D.Sc. Assistant Professor of Clinical Medicine, 
University College, Londou. 52 Upper Berkeley-street. W. 

f Brady, George Stewardson, M.D. LL.D. Professor of Natural History in 
the Durham College of Science, Newcastle. 2 Mowbray-villas, Sunderland. 

\ Bramwell, Sir Frederick Joseph, Bart., D.C.L. (Oxon. et Dun elm) LL.D. 
(Cantab, et Univ. McGill) M. Tnst. C.E. 5 Great George-street, Westminster. 
S.W. 

\ Brandis, Sir Dietrich, K.C.l.E. Ph.D. F.L.S., late Inspector-General of Forests to 
the Government of India. 21 Kaiser Strasse, Bonn, Germany. 
Brown, Alexander Cram, D.Sc. LL.D. M.D. Professor of Chemistry in the Uni- 
versity of Edinbiugh. 8 Belgrave-crescent, Edinburgh. 

* Brown, Horace T., F.C.S. F.I.C. F.G.S. 52 Nevern-square, South Kensington. S.W. 

* Browne, Sir James Crichton, Rt., M.D. LL.D. F.R.S.E. Gl Carlisle-place 

Mansions, Victoria-street. S.W . 
f Brunton, Thomas Lauder, M.D. Sc.D. (Edin.) Hon. LL.D. (Aberdeen) Coll. Reg. 

Med. Soc. 10 Stratford-pilace, Oxford-street, W. ; and Athenaeum Club. 
i= Bryan, George Hartley, M.A. Fellow of St. Peter's College, Cambridge. 

Thornlea, Chaucer-road, Trumphigton-road, Cambridge. 
t Bryce, Right Hon. James, D.C.L. 54 Portland-place. W. 

* Buchanan, John Young, M.A. F.R.S.E. F.C.S. F.R.G.S. 10 Moray-place, Edin- 
burgh. 

\ Bucknill, Sir John Charles, M.D. (Loud.) Coll. Reg. Med. Socius. Coll. Univ. 
Lond. Soc. East Cliff House, Bournemouth. 



Served on 
Council. 

'61^63 



Date of Election. 

June 11, 1857. 

Jiuie 12, 1879, 

June 5, 1890. 
June 1.1893. 

June 7. 1894. 



June 8, 1871. '77-79 



June 9. 1887. 
Dec. 14, 1882. 
June 3, 1869. 
June 7, 1894. 
Jan. 16, 1873. 



June 2, 1881. '83-85 

'89-91 



June 7, 1888 



June G, 1889. 
June 7, 1888. 



June 8, 1882. "88-90 
June G, 1872. 

June 9, 1848.! '78-80 



June 4, 18G8. 


'71-73 




'85-87 


June 4, 188G. 




June 4, 1885. 


'93-95 



R. 



FELLOWS OF THE SOCIETY. (Nov. 30, 1895.) 



Buckton, George Bowdler, F.C.S. F.E.S. F.L.S. Con-. Acad. Nat. Sci. Philad., 

Mem. Soc. Entoin. France. Weycombe, ITasleraere, Surrey. 
Buller, Sir Walter Lawiy, K.C.M.G. D.Sc, F.L.S. Z.S. (Corr.) The Terrace, 

Wellington, New Zealand. 
Burbmy, Samuel Hawksley, M.A. 17 Upper Phillimore-gardens, Kensington. W. 
Burnside, William, M.A. Professor of Mathematics, Royal Naval College, 

Greenwich. The Laurels, Hither green-lane. S.E. 
Callendar. Hugh Longbonrne, M.A. Late Fellow of Trinity College, Cambridge, 

Professor of Physics in McGill College, Montreal. McGill College, Montreal, 

Canada. 
Carruthers, William, V.P.L.S. F.G.S. Keeper of the Botanical Department, 

British Museum. Central House, Central-hill, S.E.; and British Museum (Nat. 

Hist.), Cromwell-road. S.W. 
Cash, John Theodore, M,D, Regius Professor of Materia Medica in the 

University of Aberdeen. 25 Dee-street, Aberdeen. 
Chamberlain, Right Hon. Joseph, LL.D. (Cantab.). 40 Prince' s-gardens ; and 

Athenaeum Club. S.W. 
Chambers, Charles, Director of the Colaba Observatory, Bombay. Coldba Obser- 
vatory, Bombay. „ 
Cheyne, William ' Watson, M.B. C.iM. (Edin.) F.R.C.S. (Eng.) Professor of 

Surgery in King's College, London. 75 Harley-street. W. 
Childers, Right Hon. Hugh Culling Eardley, F.R.G.S. 6 St. George's -place, 

S.W. ; Brooks's and Athenceum Clubs. S.W. 
Christie, William Henry Mahoney, M.A. F.R.A.S. F.R. Met. Soc. Astronomer 

Royal, Corr. Mem. Imp. Acad. Sci. St. Petersb. For. Memb. Roy. Acad. 

Sci. Palermo, Colt. Mem. Soc. Spettros. Ital. Soc. Nationale des Sci. 

Nat. et Math. Cherbourg-. Royal Observatory, Greenwich. S.E. 
Church, Arthur Herbert, M,A. (Oxon.) F.C.S. F.I.C. Professor of Chemistry in. 

the Royal Academy of Arts, Lecturer on Organic Chemistry, Royal Indian 

Engineering College, Cooper's Hill. Shelsley, Kew. 
Clark, Latimer, Mem. Inst. C.E. F.R.A.S. 11 Victoria-street. S.W. 
Clarke, Alexander Ross, Colonel, R.E. C.B. Hon. F.C.P.S. Hon. F.R.S.E. 

Corr. Mem. Imp. Acad. Sci. St. Petersb. Boldrewood, Redhill, Surrey. 
Clarke, Charles Baron, M.A. (Cantab.) F.L.S. F.G.S. 13 Kew Gardens-road, Kew. 
Cleland, John, M.D. D.Sc. LL.D. Professor of Anatomy in the University of 

Glasgow. University, Glasgow. 
Clerk, Henry, Major-General, R.A. 40 St. Ermin's Mansions, Ca.vton-street, 

Westminster. S.W. 
Clifford-AUbutt (see Allbutt). 
Clifton, Robert Bellamy, M.A. (Cantab, et Oxon.), F.R.A.S. Professor of 

Experimental Philosophy in the University of Oxford, Soc. Lit. Phil. Mane. 

Soc. Honor. 3 Bardie ell- road, Banbury-road, Oxford ; and Athenaum Club. 
Colenso, Rev. William, F.L.S. Hon. Mem. N.Z. Inst., Mem. Penzance Nat. Hist. 

and Antiq. Soc, Hon. Mem. Santa Barbara (Cal.) Soc. Nat. Hist. Napier, 

Nciv Zealand. 
Common, Andrew Ainslic, Treas. R.A.S. LL.D. (St. And.) D.Sc. 63 Faton-rise, 

Ealinq. W. 



10 



J)ate of Election. 


June 


4, 1891. 


June 


6, 1878. 


June 


6, 1878. 


June 


4, 1885. 


June 


4, 1868. 


June 


4, 1863. 


Apr. 


3, 1879. 


June 


4, 1891. 


June 


6, 1889. 


June 


3, 1880. 


June 


8, 1882. 


June 


12, 1879. 


Jan. 


24, 1895. 


June 


6, 1867. 



Served on 
Council. 



78-79 



'77-79 
'94-95 

'80-81 



'94-95 



'84-85 
'86-87 



'89-91 



June 4,1891. 
June 5, 1862. 



R, 
D. 



R. 



FELLOWS OF THE SOCIETY. (Nov. 30, 1895.) 

* Conroy, Sir John, Bart., M.A. F.C.S. Fellow and Bedford Lecturer of 
Balliol College, Oxford. Balliol College, Oxford. 

f Cotterill, James Henry, M.A. Professor of Applied Mechanics, Royal Naval 

College, Greenwich. 18 Gloucester-place, Greenwich. S.E. 
Crawford, James Ludovic, Earl of, K.T. LL.D., Trustee of Brit. Mus., F.R.A.S. 

Leg. Honor. Com. Ord. Imp. Bras. Rosae Com. Acad. Reg. Sci. Berol. Soc. 

Honor. 2 Cavendish-square, W. ; and Haigh Hall, Wigan. 
Creak, Ettrick William, Captain R.N. M. Inst. Elect. Eng. 36 Kidbrooke-park- 

road, Blackheath. S.E. 
Crofton, Morgan William, D.Sc. Fellow of the Royal University of Leland 

15 Ambrose-place, Worthing. 
Crookes, William — Vice-President — Past Pres. Chem. Soc. and Inst. Elect. 

Eng. 7 Kensington-park-gardens, W. ; and Athenaeum Club. S.W. 
|- Cross, Right Hon. Richard Assheton, Viscount, G.C.B. G.C.S.I. D.C.L. LL.D. 

12 Warwick-sq. and Athenceum Club, S.W. ; and Eccle Biggs, Broughton-in- 

Furness, Lancashire. 

* Cunningham, Daniel John, M.D. (Edin. and Dubl.), D.Sc. D.C.L. LL.D. Prof, of 
Anatomy in the University of Dublin. 43 Fitzwilliam-place, Dublin. 

Cunningham, David Douglas, M.B. CM. (Edin.) CLE. F.L.S. Biigade Surg. 
Lieut.-Col. Bengal Medical Service. Honorary Surgeon to the Viceroy of 
India. Professor of Physiology in the Medical College, and Fellow of the 
University of Calcutta. 9 Loudon-street, Calcutta. 

* Dallinger, Rev. William Henry, LL.D. Sc.D. (Dubl.) F.L.S. Vice-Pres. R.M.S., 

Hon. Mem. Amer. Micros. Soc. Ingleside, Neicstead-road, Lee. S.E. 
Darwin, Francis, M.A. and M.B. (Cantab.) F.L.S. F.Z.S. F.R.M.C.S. Fellow 

of Christ's College, and Reader in Botany in the Univ. of Cambridge. 

Mem. Soc. Nat. Sci. et Math, de Cherbourg. Wychfield, Huntingdon-road, 

Cambridge. 
Darwin, George Howard, M.A. LL.D. (Glasc.) Sc.D. (Dubl.) Ph.D. (Padua) 

F.R.A.S. F.M.S. Hon. Mem. R.I.A. Fellow of Trinity College and Plumian 

Professor of Astronomy and Experimental Philosophy in the University of 

Cambridge. Hon. Fell. Astron. and Phys. Soc. Toronto. Newnham 

Grange, Cambridge. 
f Davey, Right Hon. Horace, Lord, M.A. D.C.L. 86 Brook-street, W. ; and 

Verdley-place, Fernhurst, Sussex. 
f Dawkins, W. Boyd, M.A. (Oxon.) F.S.A. F.G.S. Assoc. Inst. C.E. Hon. 

Fellow of Jesus Coll. (Oxford) Professor of Geology and Palaeontology in the 

Victoria University, Owens Coll., Manchester. Soc. Anthrop. Berol. Acad. Sci. 

Nat. Philad. et Soc. Nat. Hist. Bost. Corresp. Soc. Phil. Amer. et Acad. Sci. 

Nov.Ebor. et Soc. Geol. Belg. Soc. Honor. Woodhurst, FalloxvfieM, Manchester. 

* Dawson, George Mercer, C.M.G. LL.D. F.G.S. A.R.S.M. F.R.S.C. Assistant 

Director of the Geological Survey of Canada. Sussex-street, Ottawa, Canada. 
Dawson, Sir J. William, C.M.G. M.A. LL.D. F.G.S. Late Principal and Vice- 
Chancellor of M'Gill University, Montreal, Hon. Mem. Phil. Soc. Leeds, 
Glasg., Princeton, Soc. Nat, Hist. Boston, Maryland Academy. Corresp. 
Fell. Geol. Soc. Edin., Fell. Roy. Soc. Canada, Amer. Acad. Arts and 
Sciences, Amer. Phil. Soc. Corr. Mem. Acad. Nat. Sci, Philad. 293 
University-street, Montreal. 



FELLOWS OF THE SOCIETY. (Nov. 30, 1895.) 



11 



Date of Election. 

June 6, 1861. 


Served on 
Council. 

'7(M2 
'81-83 


Mar. 3. 1892. 




June 7. 1877. 


'85^6 


June 4, 1885. 




June 4, 1886. 




June 7, 1883. 




Feb. 22, 1855. 




Feb. 9, 1865. 




June 1, 1876. 


'79-81 


June 1, 1893. 




June 3, 1875. 




June 3, 1880. 


'86-88 


June 13, 1895. 




June 12, 1873. 





Km. 



t Debus, Heinrich, Ph.D. F.C.S. Late Prof, of Chemistry at the Royal Naval 
College, Greenwich, Lecturer on Chemistry at Guy's Hospital. 4 
Schlangenweg, Cassel, Hessen, Germany. 

I" Devonshire, Spencer Compton Cavendish, Duke of, K.G. M.A. LL.D. Hon. Men.. 
Inst. C.E. Chancellor of the University of Cambridge. Devonshire House, 
Piccadilly, W. ; and Chatsworth, De?-byshi?-e. 

Dewar, James, M.A. F.C.S. F.R.S.E. Hon. LL.D. (Glasc. and St. And.) Jack- 
sonian Prof, of Natural Experimental Philosophy hi the University of 
Cambridge, Fullerian Prof, of Chemistry in the Royal Institution. 1 
Scroope-terrace, Cambridge; and Royal Institution, Albemarle-street. W. 

Divers, Edward, M.D. Professor of Chemistry in the Imperial University, Japan. 
Hongo, Tokyo, Japan. 

* Dixon, Harold B., M.A. F.C.S. Prof, of Chemistry and Director of the Chemical 

Laboratories in Owens College, Manchester. Birch Hall, Rusholme, 

Manchester. 
Douglass, Sir James Nicholas, M. Inst. C.E. M. Inst. M.E. M. Inst. E.E. Late 

Engine er-in-Cliief to the Hon. Corporation of Trinity House. Stella House, 

Dulwich. S.E. 
Ducie, Henry John Reynolds-Moreton, Earl of, F.G.S. Tortworth Court, 

Faljield, Gloucestershire. 
Dufferin and Ava, Frederick Temple Blackwood, Marquis of, K.P. G.C.B. 

G.C.M.G. G.C.S.I. G.M.I.E. D.C.L. (Oxford) LL.D. (Camb. and Dubl.) 

F.R.G.S. Clandeboye, Co. Down, Ireland. 
f Dunkin, Edwin, F.R.A.S. Formerly Chief Assistant, Royal Observatory, Green- 
wich. Kenwyn, Kidbrooke Park-road, Blackheath. S.E. 

* Dunstan, Wyndham R., M.A. (Oxon.) Sec. Chem. Soc. F.I.C. Professor of 

Chemistry to, and Director of the Research Laboratory of, the Pharma- 
ceutical Society of Great Britain. Lecturer on Chemistry at St. Thomas's 
Hospital. 3 Percy-villas, Campden Hill, Kensington. W. 
t Dupre, August, Ph.D. F.C.S. Lecturer on Chemistry at the Westminster 
Hospital. Westminster Hospital Medical School, Caxton-street, Westminster, 
S.W. ; and Cliftonville, Sutton, Surrey. 

* Dyer, William Turner Thiselton, C.M.G. CLE. M.A. (Oxon.) B.Sc. (Lond.) Ph.D. 
F.L.S. Director, Royal Gardens, Kew; late Fellow Univ. of London; Hon. 
Fellow, King's Coll., Lond. ; Bot. Soc. Edin. ; Hon. Mem. Roy. Bot. Soc. 
Lond., Pharm. Soc. Gt. Britain ; Cam. Phil. Soc. ; Lit. Phil. Soc. Manchester; 
Soc. Neerland d'Hort. et de Bot., Amsterdam and New Zealand Institute ; 
Corresp. Acad. Sci. Philad. ; Boston Soc. Nat. Hist. ; Hort. Soc. Berlin 
and Massachusetts; Soc. Nat. Sci. et Math, de Cherb. ; and Botan. Soc. 
Copenhagen ; Mitg. Kais.-Leop. Deutsch. Acad, der Naturf. in Halle. 
Royal Gardens, Kew. 

* Eliot, John, M.A. Meteorological Reporter to the Government of India. Indian 

Meteorological Office, Simla. 
t Ellery, Robert Lewis John, C.M.G. F.R.A.S. Late Government Astronomer, 
and Director of the Observatory. Melbourne, Victoria. 

B 2 



u 

Date of Election. 

June 4, 1891 

Juno 1, 1893. 

June 1, 1876. 

June ?, I860. 

June 8, 1871. 

June 2, 1864. 



Served on 

Council. 



'84-85 



'67-G8 
'7; J ,-75 
"78-95 



June 12. 1679. 

June 1, 1893. 

June 9, 1SS7. 

June 7, 18GG. 

June 7, 1877. 

June 7, 1877. 

June 1, 1876. 

June 4, 188(3. 

June 7, 1883. 

June 2, 18?2 



'80-88 



R. 



R. 



FELLOWS OF THE SOCIETY. (Nov. 30, 1895.) 

* Elliott, Edwin Bailey, M.A. E.R.A.S. Wayuflete Professor of Pure Mathematics 
in the University of Oxford; Fellow of Magdalen College, Oxford. 4 
Bardivell-road, Oxford. 

Ellis, William, F.R.A.S. F.R. Met, Soc. Memb. Inst. Elect. Eng. Late Super- 
intendent of the Magnetical and Meteorological Department, Royal 
Observatory, Greenwich. 12 Yanbrugh-hill, Blachheath. S.E. 

Erichsen, Sir John Eric, Bart.,F.R.GS. LL.D. (Edin.) Sm-geon Extraordinary to 
the Queen, Pres. of and Emeritus Prof, of Surgery to University College, and 
Consulting Surgeon to the Hospital. 6 Cavendish-place, Cavendish-square. W. 

Esson, William, M.A. F.C.S. F.R.A.S. Deputy Savilian Professor of Geometry 
in the University of Oxford, Fellow, and Mathematical Tutor of Merton 
College. Merton College; and 13 Brudmore-road, Oxford. 

Etheridge, Robert, F.R.S.E. F.G.S. Hon. Memb. Geol. Soc. Belg. N.Z. Inst. 
Roy. Geol. Soc. Cornwall, Phil. Soc. York, Bristol, Corresp. Imp. Geol. 
Inst. Vienna, 14 CarlyLc-square, Chelsea. S.W. 

Evans, Sir John — Treasurer and Vice-President — K.C.B. D.C.L. (Oxon.) 
LL.D.(Dubh) Sc.D.(Camb.) Trustee, Brit. Mus. F.S.A. F.L.S. F.G.S. F.C.S. 
F.Z.S. Assoc. I.C.E. Pres.Num.Soc. Hon.M.R.I.A. Hon. F.S.A. (Scot.) Comm. 
of the Ord. of St. Thiago of Port., Cor, of Inst, de France (Acad, deslnscrip.), 
Hon. Mem. of the Amer. Phil. Soc., Amer. Acad. Arts and Sciences, Amer. 
Ethnol. Soc., Num. and Ant, Soc, of Philadelphia, Amer. Num. and 
Archteol. Soc, Soc Franc, de Numism., Soc. Ital. d'Anthrop., Soc. Roy. 
Gr. Due. de Luxembourg, Soc. Anthrop. de Brux. et de Lyons, Soc. de 
Borda. Dax., Soc. Polym. du Morbiban, and Soc. Suisse de Numism., For. 
Mem. of the Soc. Ant. of Sweden, Soc. Anthrop. de Paris, and the Numism. 
Soc. of the Netherlands, and Corr. Mem. of the Soc. Geol. de Belg., Inst, 
di Corr. Arch., Acad. Yaldarn., Anthrop. Soc. of Berlin, and Soc. d'Emui. 
d' Abbeville. Nasli Mills, Ilemcl Hempstead ; and A thenanim Club. 

* Everett, Joseph David, M.A. D.C.L. F.R.S.E. Professor of Natural Philosophy in 

Queen's College, Belfast, Derryvclgie Avenue, Belfast. 

* Ewart, James Cossar, M.D. Professor of Natural History in the University of 

Edinburgh. The University, Edinburgh. 

* Ewing, James Alfred, Hon. M.A. (Canib.) B.Sc. (Edin.) F.R.S.E. M. Inst. C.E. 

Professor of Mechanism and Applied Mechanics in the University of Cam- 
bridge. Langdale Lodge, Cambridge. 

f Farrar, Very Rev. Frederic William, M.A. D.D. (Cantab.) Dean of Canterbury. 

t Fayrer, Sir Joseph, K.C.S.I. M.D. LL.D. (Edin. and St. And.) F.R.C.P. (Lond.) 
F.R.C.S. F.R.S.E. Honorary Physician to the Queen. 16 Devonshire-street, 
Portland-place. W. 
Ferrers, Rev. Norman Macleod, D.D. Master of Gonville and Caius College, 

Cambridge. The Lodge, Gonville and Caius College, Cambridge. 
Ferrier, David, M.A. (Aberd.) M.D. (Edin.) LL.D. F.R.C.P. Professor of 
Neuro-pathology, King's College, London. 34 Cavendish-square. AY. 

* Festing, Edward Robert, Major-General, R.E. (retired). Science Museum 

Director, South Kensington Museum. South Kensington. S.W. 

* Fitzgerald, Prof. George Fraucis, M.A. D.Sc. 40 Trinity College, Dublin. 

* Fleming, John Ambrose, M.A. (Camb.) D.Sc (Lond.) Late Fellow of St. John's 

College, Cambridge, Fellow and Professor of Electrical Engineering in 
University College, London. University College, Gower-street. W.C. 



FELLOWS OF THE SOCIETY. (Nov. 30, 1895.) 



13 





Served on 




Dale of Election. 


Council. 




June ~J, 1889. 






June 2, 1864. 


'68-70 
'76-78 
'84-86 


B. 



June 9. 1887. 



June 4. 1886, 



June 2. 1892. 



June 3, 1869 



June 6. 1872. 



June 2. 1853 



June 4. 1891 



'93-95 



'70-72 
'77-78 
'83-85 
"91-93 
'76-77 
'81-95 



'57-59 
'65-67 
'75-77 

'86-88 



C. 

B. 



Fletcher, Lazarus, M.A. (Oxon.) F.G.S. F.C. S. Keeper of Minerals in the 

British. Museum. Natural History Museum, Cromwell-road; and 36 Wood- 

ville-road, Ealing. W. 
Flower, Sir William Henry, K.O.B. D.C.L. (Oxon. et Dunelm.) LL.D. (Edin. 

et Dubl.) Sc.D. (Camb.) Ph.D. (Utrecht) F.E.C.S. P.Z.S. F.L.S. F.G.S. V.P. 

Anthrop. Inst. Hon. Fell. Boy. Med. Chir. Soc. Hon. Memb. Asiat. Soc. 

Bengal, Camb. Phil. Soc, Manchester Lit. Phil. Soc. N.Z. Inst, Zool. Soc. 

Amsterdam and France, Acad. Sci. New York, Anthrop. Soc. Washington, 

Memb. Amer. Phil. Soc. Imp. Soc. Nat, Moscow, Corresp. Memb. Inst, Fr. 

(Acad. Sci.) Acad. Sci. Bologna, Acad. Sci. Turin, Acad. Nat. Sci. Philacl., 

Soc. Nat. Hist, Boston, Soc. Anthrop. Ethnol. and Prehist. Arch. Berlin. 

Anthrop. Soc. Borne, For. Assoc. Anthrop. Soc. Paris, Director of the Nat. 

Hist. Departments, British Museum. Natural History Museum. Cromurll- 

road; and 26 Stanhope-gardens. S.W. 

* Forbes, George, M.A. F.E.S.E. F.E.A.S. Mem. Inst. C.E. M.I.E.E. Chew Leg- 

Honor. Memb. Astron. Gesell. Vienna, Amer. Phil. Soc, and Franklin Inst. 
Formerly Professor of Nat. Phil, in Anderson's College. Glasgow. 34 Great 
George-street. S. W. 

* Forsyth, Andrew Eussell, M.A. Sc.D. F.C.P.S. Sadleiian Professor of Pure 

Mathematics in the University of Cambridge, Fellow of Trinity College, 
Cambridge. Trinity College, Cambridge. 

* Foster, Clement Le Neve, B.A. D.Sc. (Lond.) F.G.S., A.E.S.M., Professor of 

Mining in the Eoyal College of Science, and H.M. Inspector of Mines. 
Min-y-don. Llandudno. 
Foster, George Carey, B.A. F.C.S. Professor of Physics in University College, 
London. 18 Daleham-gardens, South Hampstead, N.W. ; and Athenaeum 
Club. S.W. 

t Foster, Michael— Secretary— M.D. B.A. (Lond.) Hon. M.A. (Cantab.) D.C.L. 

(Oxon.) LL.D. (Glasg. and St. And.) Sc.D. (Dubl.) F.L.S. F.C.S. For. 

Mem. E. Accad. dei Lincei, Borna, E. Accad. delle Scienze, 

Torino, Hon. Mem. Eoy. Irish Acad., Lit, and Phil. Soc. Mane, 

Eoy. Soc. N. S. Wales, Med. Chir. Soc, and Pharm. Soc Lond., 

Professor of Physiology in the University of Cambridge. Great Shelford, 

Cambridge. 
Frankland, Edward — FOREIGN SECRETARY — D.C.L. (Oxon.) Ph.D. (Marp.) M.D. 

(Wiirzburg) LL.D. (Edin. et Univ. McGill) V.P.C.S. Hon. Mem. Inst, C.E., 

Assoc. Etrang. Inst. Fr. (Acad. Sci.) Par., Imp. Sci. Petrop. et Vindob. 

Eeg. Sci. Berol. Soc. pro fov. Indust. Nat. Corresp., Soc. Eeg. Sci. 

Gott. et Upsal, Soc. Nat. Scrutat Hehet,, Acad. Eeg. Monac Socius 

Honor., Soc. Eeg. Edin. Acad. Eeg. Hib., Soc. Lit. Phil. Mane, Soc. 

Chem. Berol. et Acad. Sci. Amer. Nov. Ebor. Lehigh Univ. U.S. Soc. 

Eeg. Sci. Boie. Marob. et Nat. Sanit. Dresd., Chem. Amer. Nov. Ebor. 

Soc. Eeg. Med. Chi. Lond. et Adsoc. Intern, pro Hyg. promov. Brux. 

Soc. Asiat, Beng. Soc. Honor. The Yews, Reigate-hill, Reigate ; and 

Athenamm Club. 
Frankland, Percy Faraday, Ph.D., B.Sc, A.E.S.M. Professor of Chemistry in 

the Mason College. Birmingham. Mason College, Birmingham. 



14 



Date of Election. 


Served on 
Council. 


June 


4, 1874. 




June 


7, 1877. 




June 


7, 1883. 




June 


7, 1894. 




Dec. 


13, 1883. 




June 


2, 1892. 




June 


1, 1893. 




June 


9, 1859. 


'61-63 
'67-69 
'94-95 


June 


7, 1860. 


'65-66 
'70-72 
'76-77 
'82-84 


June 


6, 1872. 


'86-88 


June 


5, 1890. 




June 


3, 1858. 




June 


8, 1882. 




June 


1, 1865. 


'85-87 
'89-93 



R. 



R. 



FELLOWS OF THE SOCIETY. (Nov. 30, 1895.) 

t Franks, Sir Augustus Wollaston, K.C.B. D.C.L. (Oxon.) P.S.A. F.G.S. Trust. Brit. 
Mus. Keeper of British and Mediaeval Antiquities, and of Ethnography at 
the British Museum. British Museum, W .C. ; and 123 Victoria-street, West- 
minster. S.W. 

f Fraser, Thomas Richard, M.D. (Edin.) F.R.C.P. & R.S. (Edin.) LL.D. (Aherdeen) 
Professor of MateriaMedica and Clinical Medicine in the University, Edin- 
burgh. 13 .Drumsheugh-gardens, Edinburgh. 

* Frost, Percival, Sc.D. Fitzwilliam-street, Cambridge. 
Froude, Robert Edmund. Superintendent of the Admiralty Experimental 

Works, Gosport. 1 Claremont, Alverstoke, Gosport. 
Fry, Right Hon. Sir Edward, B.A. (Lond.) D.C.L. (Oxon.) LL.D. (Edin.) 

F.S.A. F.L.S. Fellow of the University of London, and of University 

College, London, and Hon. Fellow, Bailiol Coll. Oxon. Failand House, 

Failand, near Bristol. 
Gadow, Hans Friedrich, Ph.D. (Jena) Hon. M.A. (Camb.) Strickland Curator 

and Lecturer on the Advanced Morphology of Vertebrata in the University 

of Cambridge. Zoological Laboratory, Cambridge. 

* Gairdner, William Tennant, M.D. (Edin.) Hon. M.D. (Dubl.) Hon. LL.D. (Edin.) 
F.R.C.P. (Edin.) Hon. F.R.C.P. (Irel.) Professor of Medicine in the Uni- 
versity of Glasgow. Physician in Ordinary to the Queen in Scotland. 
The University, Glasgow. 

Galton, Sir Douglas, K.C.B. D.C.L. LL.D. (Univ. McGill and Durham) F.G.S. 

F.L.S. F.C.S. F.R.G.S. Hon. Memb. Inst. C.E. 12 Chester-street, Grosvenor- 

place. S.W. 
Galton, Francis, M.A. (Cantab.) D.C.L. (Oxon.) Sc.D. (Camb.) Officier de 

lTnstruction Publique, France; Corresp. Memb. of the Geograph. 

Societies ot Berlin and Vienna, and of Anthrop. Soc. of Rome. Hon. 

Memb. of Geograph. Soc. of Italy, and Inst. Internat. de Statistique. 

42 Rutland-gate. S.W. 
Gamgee, Arthur, M.D. M.R.C.P. (Lond.) & F.R.C.P. (Edin.) 8 Avenue de la 

Gare, Lausanne, Switzerland. 
Gardiner, Walter, M.A. F.L.S. Fellow of Clare College, Cambridge, and 

University Lecturer in Botany. 45 HilFs-road, Cambridge. 
f Garrod, Sir Alfred Baring, M.D. Coll. Reg. Med. Socius, Physician Extraordinary 

to the Queen, Consulting Physician to King's College Hospital. 10 Harley- 

street. W. 

* Gaskell, Walter Holbrook, M.A. M.D. (Cantab.) LL.D. (Edin.) Lectiuer in 

Physiology at Cambridge. The Uplands, Great Shelford, near Cambridge. 
\ Geikie, Sir Archibald, Knt. Sc.D. (Cantab, et Dubl.) LL.D. (Edin. et St. And.) 
F.R.S.E. F.G.S. F.Z.S. Director-General of the Geological Survey of the 
United Kingdom, and of the Museum of Economic Geology, London. — 
Inst. Franc. (Acad. Sci.) Acad. Reg. Berol. Acad. Imp. Sci. Vindob. Acad. 
Reg. Bavar. Monach. Soc. Cor. ; Soc. Reg. Sci. Gottingen ; Caesar. Leop. 
Carol. Acad. Sci. Nat. ; Soc. Imp. Mineral. Petropol ; Soc. Imp. Nat. Sci. 
Mosquen ; Acad. Reg. Valdarnese del Poggio ; Soc. Geogr. Ital. et Batav. ; 
Soc. Geol. Edin. Glasc. Liverp. Manchest. Franc. Belg. Stockholm; Soc. 
Phil. Ebor. et Americ, Soc. Sci. Christiania, Socius. Geological Survey Offi.ce, 
28 Jermyn-slreet, S.W. ; 10 Chester-terrace, Regent's Park. N.W. 



Date of Election. 

June 3, 1875 



Served on 
Council. 



FELLOWS OF THE SOCIETY. (Nov. 30, 1895.) 



15 



June 2, 1892. 
June 7, 1860 



June 4, 1891 
June 7, 1883. 



'86-88 



June 2, 1853 

Jan. 13, 1881 
June 7, 1849 

June 3, 1875 

June 8, 18S2. 

June 8, 1882. 



'63-64 
'66-68 



'83-84 
'90-92 

'92-94 

'91-93 



June 


3, 1880. 


June 


1, 1865. 


Jan. 


18, 1872. 


June 


2, 1892. 


June 


9, 1887. 



Feb. 3, 1881. 



fGeikie, James, D.C.L. (Dunelm.) LL.D. F.R.S.E. F.R.G.S. F.G.S. Murchison, 
Professor of Geology and Mineralogy in the University of Edinburgh, Hon. 
Memb. Phil. Soc. York, Geol. Soc. Stockholm, Vidensk.-Selsk. Christiania, 
Geol. Palfeont. Hydrol. Belg., Soc. Geol. Neuehatel, Memb. Amer. 
Phil. Soc. Corresp. Memb. Acad. Sci. Philadelphia. 31 Merchiston-avenue, 
Edinburgh. 

Giffen, Sir Robert, K.C.B. LL.D. (Glasc.) 44 Pembroke-road, Kensington. W. 

Gilbert. Sir Joseph Henry, M.A. (Oxon.) Sc.D. (Camb.) Ph.D. (Giessen) LL.D. 
(Edin. et Glasc.) Sc.D. (Cantab.) V.P.C.S. F.L.S. Soc. Reg. Agric. Engl. 
Soc. Honor. Inst. Fr. (Acad. Sci.) Mem. Cor. Soc. Chem. Agric. Ult. et 
Acad. Agric. et Sylv. Petrovsk. et Soc. Reg. Agric. Hannov. Soc. Honor. 
Soc. pro. fov. Ind. Nat. Par. Soc. Agric. Franc, et Inst. Agron. Gorigoretsk. 
Mem. Corr. Acad. Reg. Agric. Sued. Soc. Late Sibthorpian Professor of 
Rural Economy in the Univ. of Oxford. Harpmden, St. Albans ; and 
Athenceum Club. 

Gilchrist, Percy Carlyle, A.R.S.M. Frognal Bank, Finchley-road, Ramp- 
stead. N.W. 

* CHI, David, LL.D. (Aberd. et Edin.) Hon. F.R.S.E. F.R.A.S. F.R.G.S. Her 
Majesty's Astronomer at the Cape of Good Hope, Trustee, S. African 
Museum, Corresp. Mem. Imp. Acad. Sci. S. Petersb., and Roy. Acad. Sci. 
BerL, For. Mem. Soc. Holl. des Sci., Haarlem; Corresp. Mem. Soc. degli 
Spettroscop. Ital. Rome, Soc. Nationale des Sci. Nat. et Math. Cherbourg, 
Geogr. Soc. Lisbon. Royal Observatory, Cape of Good Hope. 

Gladstone, John Hall, Ph.D. Sc.D. (Dubl.) V.P.C.S. 17 Pembridge-square. 

W. 
t Gladstone, Right Hon. William Ewart, D.C.L. Hawarden, Chester. 

Glaisher, James, F.R.A.S. Ord. Bras. Rosae Eq. The Shola, Heathfield Road, 

South Croydon. 
Glaisher, James Whitbread Lee, Sc.D. (Camb. and Dubl.) V.P.R.A.S. F.C.P.S. 

Trinity College, Cambridge. 

* Glazebrook, Richard Tetley, M.A. Treas. C.P.S. Fellow of Trinity College, Cam- 
bridge. 7 Harvey-road, Cambridge. 

Godman, Frederick Ducane, F.L.S. F.G.S. F.E.S. 10 C%andos-street, Cavendish- 
square, W. ; and South Lodge, Horsham. 

Godwin-Austen, Henry Haversham, Lieut.-Col. F.G.S. F.Z.S. F.R.G.S. Shal- 
ford House, Guildford. 

Gore, George LL.D. (Edin.). Inst. Sci. Research, 67 Broad-street, Birmingham. 

Goschen, Right Hon. George Joachim, M.A. 69 Portland-place. W. 

* Gotch, Francis, B.A. B.Sc. (Lond.) Hon. M.A. (Oxon.) M.R.C.S. Waynflete 
Professor of Physiology in the University of Oxford. The Lawn, Banbury- 
road, Oxford. 

* Gowers, William Richard, M.D. F.R.C.P. Fellow of University College, 
London, Consulting Physician to University College Hospital. Physician 
to the National Hospital for the Paralysed and Epileptic. 50 Queen Anne- 
street. W. 

! t Grant Duff, Right Hon. Sir Mountstuart Elphinstone, G.C.S.I. V.-P.R.G.S. 
Athenreum Club; and York House, Twickenham. 



1(3 

DateofElection. S ^™ 

June 4, 1S86. '93^95 
June 13, 1895 



June 7, 1888. 

June 6, 1878. 
June 13, 1895. 

Nov. 26, 1840. "45-50 
'56-58 
'61-62 
'66-67 
'78-79 

June 7, 1883. 

June 7, 1883. 

June 6, 1867. '74-76 



R. 



June 4, 1891. 
Jan. 13, 1887. 
June 4, 18G8. 

Dec. 15. 1881. 
June 1. 1865. 
June 4, 1863. 
June 12, 1884 

June 3, 1858. 
June 2, 1864. 



78-SO 



E. 



FELLOWS OF THE SOCIETY. (Nov. 30, 1895.) 

* Green, Alexander Henry, M.A. Professor of Geology in the University 

of Oxford. University Museum, Oxford. 

* Green, Joseph Reynolds, M.A. B.Sc. (Lond.) D.Sc. (Camb.) F.L.S. Professor 

of Botany to the Pharmaceutical Society of Great Britain. Arncliffe, 
Gra nge-roa d, Cam bridge. 

* Greenhill, Alfred George, M.A. Professor of Mathematics in the Artillery College, 

Woolwich. 10 New Inn. W.C. 
h Green-well, Rev. William, M.A. D.C.L., Canon of Durham, F.S.A. Durham. 

* Griffiths, Ernest HoAvard, M.A. 12 Parhside, Cambridge. 

Grove, Right Hon. Sir William Robert, Knt., M.A. D.C.L. (Oxon.) LL.D. 
(Cantab.) Hon. F.R.S.E. Hon. Mem. Inst. C.E. Ord. Imp. Rosas Brazil 
Eq. Acadd. Reg. Sci. Taurin., Lync. Romse, Soc. Phil. Basil, et Soc. 
Imp. Carob. Corresp. 115 Barley-street. W. 

* Groves, Charles Edward, F.C.S. F.I.C. 352 Kennington-road. S.E. 

h Grubb, Sir Howard, F.R.A.S. 51 Kenilwortlt-square, Ratlwar, Dublin. 
Giinther, Albert C. L. G., M.A. M.D. Ph.D. F.L.S. F.Z.S. Late Keeper of the 

Zoological Department in the British Museum, Reg. Scient. Soc. Tlpsal 

Soc. Phys.-Med. ad Rhenuin infer. Soc. Zool.-Bot. Vindob. Socius 

ord. Reg. Acad. Panormit. Scient. Soc. Asiat, Bengal. Instit. Nov. Zel. 

Soc. Linn. Nov. Gall. Soc. Nat. Scrutat. Basil. Soc. Zool. Gall. Soc. 

Lit. et Phil. Liverpool Soc. Roman. Zoolog. Socius rlonor. Imp. Acad. 

ScK-nt. Petropcl. Reg. Acad. Scient. Taurin. Reg. Acad. Scient. Suec. 

Soc. Senckenb. Nat. Scrutat. Francci, Acad. Scient. nat. Philad. Acad. 

Scient. nat. Caiifom. Soc. Scient. nat. Cherbourg Soc. Human, et Scient. 

Gall. Merid. Orient. Soc. extran. Lichfield Iiozd, Kew Gardens, 

Surrey. 
■ Halliburton. William Dobinson, M.D. B.Sc. Professor of Physiology in King's 

College, London. 9 Ridgmount-gardens, Gower-street. "W.C. 
Halsbmy, Right. Hon. Hardinge Stanley Giffard, Lord, M.A. D.C.L. 4 Ennis- 

more-gardens. W. 
Harcourt, Augustus George Vernon, M.A. (Oxon.) D.C.L. (Dunelm.) LL.D. 

(Univ. McGill) F.C.S., Lee's Reader in Chemistry at Christ Church. Cowley 

Grange, Oxford; and Athenccum Club. S.W. 
Harcourt, Right Hon. Sir "William George Granville Venables Vernon, Knt., M.A. 

Mai wood, Lyndhurst, Hants. 
Harley, George.' M.D. F.R.C.P. F.C.S. Acad. Sci. Monach. et Soc, Phys. Med. 

Herbip. et Acad. Med. Chir. Madrit. Corr. Mem. 25 Harley-street. "W. 
Harley, Rev. Robert, M.A. (Oxon.) F.R.A.S. Lit. et Phil. Soc. Mane. Soc. Reg. 

Queensl. Soc. Honor. Rosslyn, Westlourne-road, Forest-hill. S.E. 

* Hartley, Walter Noel, F.R.S.E. F.I.C. Professor of Chemistry in the Royal College 

of Science for Ireland. Royal College of Science, Stephens-green, Dublin ; 

and 36 Waterloo-road, Dublin. 
Haughton, Rev. Samuel, M.D. (Dubl. et Bonon.) D.C.L. (Oxon.) LL.D. (Cantab. 

et Edin.) Fellow of Trinity College, Dublin. Trinity College, Dublin. 
Hay, Right Hon. Sir John Charles Dalrymple, Bart., Admiral, K.C.B. D.C.L. 

(Oxon.) F.R.G.S. V.P. Inst. Naval Architects. 108 St. George' s-squarr, SAV . ; 

ajid Craigenveoch, Wigtownshire, N.B. 



FELLOWS OF THE SOCIETY. (Nov. 30, 1895.) 



17 



P3te of Election. 

June 1, 1876. 
June 4. 1891. 
June 7, 186*3 



Served on 
Council. 



June 6, 1889. 
June 3, 1875. 

June 3, 1858. 
June 4, 1874. 

June 2, 1892. 
June 12, 1884. 

June 8,1871. 
Jan. 21, 1892. 
June 13, 1895. 
Feb. 1, 1839. 
June 4, 1885. 
June 5, 1862. 
June 4, 1885 

June 13, 1895. 



'82-83 



t Hayward, Robert Baldwin, M.A. Ashcombe, Shanklin, Isle of Wight. 

* Heaviside, Oliver, Hon. Mem. Lit. Phil. Soc. Manchester. Paignton, Devon. 
Hector, Sir James, K.C.M.G. Ord. Cr. Pruss. M.D. F.G.S. F.L.S. F.R.S.E. 

C.M.Z.S., Hon. Mem. of the Royal Societies of Victoria, New South Wales, 
South Australia, and Tasmania ; For. Mem. Amer. Acad. Sci., Amer. Inst. 
Mining Engs., and K. Leop. Carol. Acad. ; Director of the Geological 
Survey, Colonial Laboratory, Meteorological and Weather Departments, 
and of the New Zealand Institute ; Chancellor of the New Zealand 
University. Wellington, New Zealand. 

* Hemsley, William Botting, A.L.S. Hon. Memb. Nat. Hist. Soc. Mexico, Principal 
Assistant in the Herbarium, Royal Gardens, Kew. Herbarium, Royal 
Gardens, Kew. 

Hennessey, John Baboneau Nickterlien, CLE. M.A. F.R.A.S. F.R.G.S. late 

Deputy Surveyor-General in charge of the Trigonometrical Siuveys, 

Survey of India. Merrimu, 18 Alleyn-park, West Buhvich, S.E. ; and 

Athenceum Club. S.W. 
Hennessy, Henry G., M.R.I.A. Professor of Applied Mathematics and Mechanism 

in the Roy. Coll. of Science for Ireland. Clarens, Montreux, Switzerland. 
j" Henrici, Olaus Magnus Friedrich Ercimann, Ph.D. LL.D. (St. And.) Professor of 

Mechanics and Mathematics in the City and Guilds of London Institute. 

Central Technical College, Exhibition-road, S.W. ; and 34 Clarendon-road, 

Nottinghill W. 
Herdman, William Abbott, D.Sc. F.R.S.E. F.L.S. Professor of Natural History 

in University College, Liverpool. University College, Liverpool. 
Herschel, Alexander Stewart, M.A. Hon. D.C.L. (Durham), F.R.A.S. Honorary 

Professor of Physics and Experimental Philosophy in the Durham 

College of Science, Newcastle-on-Tyne. Observatory House, Slough, 

Bucks. 
Herschel, John, Col. R.E. F.R.A.S. Late Deputy Superintendent. Great 

Trigonometrical Survey of India. Observatory House, Slough, Bucks. 
Herschell, Right Hoa. Fairer, Lord, G.C.B. D.C.L. LL.D. Chancellor of the 

University of London. 46 Grosvenor-gardens. S.W. 
Heycock, Charles Thomas, M.A. - Lecturer on Natural Science, King's College, 

Cambridge. 24 Fitzwilliam-street, Cambridge. 
Heywood, James, M.A. F.G.S. F.S.A. 26 Kensington Palace-gardens, W. : and 

Athenamm Club. S.W. 
Hicks, Henry, M.D. M.R.C.S. F.G.S. Corresp. Memb. Acad. Nat. Sci. Philad.. 

Geol. Soc. Liverpool. Hendon-grove, Hendon. N.W. 
\ Hicks, John Braxton, M.D. (Lond.) F.L.S. Coll. Reg. Med. Soc. 'lhe Brackens, 

Lymington, Hauls, 
Hicks, William Mitchinson, M.A. D.Sc. Late Fellow of St. John's College, 

Cambridge, Principal and Professor of Physics in Firth College, Sheffield. 

Bunheved, Endcliffe-crescent, Sheffield. 
* Hickson, Sidney John, D.Sc. (Lond.) M.A. (Camb.) Hon. M.A. (Oxon.) F.L.S. 

Fellow of Downing College, Cambridge; Professor of Zoology in Owens 

College, Manchester. Ellesmere House, Wihnslou- Road, Fallowfield, Man- 
chester. 

C 



18 

1 Served on 
Tate of Election, i Council. 

June 7, 1894. 

June 6, 1872.! 
June 4. 1803.; '76-78 



June 7, 1855 
June 1, 1893 



June 13, 1895. 

Apr. 22, 1847/ '53-54 

| '56-58 

'62-64 

'70-80 

'84-86 



FELLOWS OF THE SOCIETY. (Nov. 30, 1895.) 



June 6, 1878. '86-87 
! '91-93 
June 4, 1886 



June 1, 1893. 
June 12. 1884- 



June 6. 1889. 

June 1, 1S65.J 'G6-68 
'69-71 

"80-82 
, '88-89 



t 
K. t 



C. 

I!. 

Dw. 



It. 
R. 



Km. 
R. 



June 3, 1S80. 



R. 



Hill, Mieaiah J. M., M.A., D.Sc. Professor of Mathematics, University College, 

London. 27 Parliament-hill-road, Hamp&tead. N.W. 
Hincks, Rev. Thomas, B.A. (Lond.) Stohelelgh, Leigh Woods, Clifton, Bristol. 
Hind, John Russell, LL.D. (Glasc.) F.R.A.S. Inst. Fr. (Acad. Sci.) Par. 

et Acad. Imp. Sci. Petrop. Corr., late Superintendent of the Nautical 

Almanac. 3 Cambridge Park-gardens, Tioickenham. 
Hippisley, John, F.R.A.S. Athenceum Club, S.W. ; and Stoneaston Park, Bath. 
Hobson, Ernest William, D.Sc. Fellow of Christ's College, Cambridge, lite 

Gables, Mount Pleasant, Cambridge. 
Holden, Henry Capel Lofft, Major, R.A. The Eaves, Belcedere, Woolwich. 
Hooker, Sir Joseph Dalton— Past President— K.C.S.I. C.B. M.D. D.C.L. 

LL.D. F.L.S. F.G.S. F.R.G.S. Hon. Mem. Roy. Bot. Soc. and Roy. Med. 

Chit - . Soc., London ; Bot. and Med. Socs., Edin. ; Nat. Hist. Soc. Newcastle; 

Camb. Philos. Soc. ; Asiat. Soc. Beng. ; and New Zeal. Institute. Corresp. 

Mem. of Acad. Sci., Paris (Sect. Botan.). Member of Acad. Imp. Sci., St. 

Petersb. ; K. Akad. der Wissensch., K. K. Geogr. Gesell., and Hort. Soc. of 

Vienna ; K. Akad. der Wissensch. Berlin ; Accad. delle Sci. dell' Istit. 

Bologna : Acad. Roy. des Sci. Brussels ; Reale Accad. dei Georgofili, 

Florence ; Kong. Dansk. Vidensk. Selsk. Copenh. ; K. Gesell. der Wiss. 

Gott. ; K. Danske Vidensk. Selskab., Stockholm ; K. Vetensk. Soc, Upsala ; 

K. Phys-oekonom. Gesell. KSnigsb. ; Soc. Vellosiana, Rio de Janeiro ; 

K. Leopcld.-Carol. Deut. Akad. der Naturf., Halle ; Senck. Naturf. Gesell. 

Frankf. a M. ; K. Baier. Bot. Gesell., Ratisb. ; R. Accad. dei Lincei, Rome ; 

Amer. Acad, of Sci., Boston. Corresp. Mem. of Dubl. Nat. Hist. Soc. and 

Agricult. Soc. of Paris. For. Mem. of Acad, de Med., Paris and Nat. Acad. 

of Sci., Washington. The Camp, Sunningdale, Berkshire. 
Hopkinson, John, M.A. D.Sc. Hohuwood, Wimbledon. S.W. 

Horsley, Victor Alexander Haden, B.S. F.R.C.S. M.D. (Halle) Professor of 

Pathology in University College, London. 25 Cavendish-square, W. ; and 

Athenceum Club. S.W. 
Howorth, Sir Henry Hoyle, K.C.I.E. D.C.L. 30 Collin gham-place, Cromwell-road. 

S.W. 
Hudleston, Wilfrid H.. M.A. F.G.S. F.C.S. 8 Stanhope-gardens, South Kensington. 

S.W. 
Hudson, Charles Thomas, M.A. LL.D. (Camb.). 2 Barton-terrace, Dawlish. 
Huggins, William — Vice-President — D.C.L. (Oxon.) LL.D. (Cantab. Edin. 

Dubl. et St. And.) Ph.D. Lugd. Bat. Hon. F.R.S.E. F.R.A.S. Ord. Imp. Bras. 

Rosae Com. Inst. Fr. (Acad. Sci.) Soc. Reg. Sci. Gott. et Soc. Spettros. Ital. 

Mem. Corr. Acad. Lync. Ronias Soc. Acad. Amer. Art. et. Sci. Boston. Reg. 

Sci. Hafn. Physiogr. Lund. Reg. Boie. Marob. Acad. Reg. Sci. Acad. Reg. 

Hib. Soc. Reg. Dubl. Lit. Phil. Mane, Soc. Astr. de France, Soc. Astr. et 

Phys. Toronto, Soc. Hist. Dallas et Soc. Reg. Nov. Camb. Austr. Soc. Honor. 

90 Upper r lulse-Mll ; and Athenceum Club. S.W. 
Hughes, David Edward, Com. of the Leg. d'Honn. Fr. and Com. of Ords. of 

Charles III. Spain, Iron Crown Austr., SS. Anne Russ., Mich. Bav., Maur. et 

Lazar. Ital. and Medijie Turkey, Past-Pres. Soc. Teleg. Eng. 40 Langham- 

strcet. Portland -place. W. 



Date of Election. 



I Served on 



FELLOWS OF THE SOCIETY. (Nov. 30, 1895.) 



19 



June 6, 1889, 



June G, 1867 



June 9, 1859. 70-71 



June 8, 1882. 



June 2, 1892 






June 6, 1878. 

Feb. 5, 1891. 

June 4, 1885. 

June 2, 1864. 

June 7, 1888, 

June C h 1872 



June 2, 1892, 
June 7. 1894, 



June 6. 1872 



* Hughes, Thomas McKeimy, M.A. Tiin. Coll. Camb. F.G.S. F.S.A. Professorial 

Fellow of Clare College, Camb., Chev. Ord. SS rum - Maur. et Lazar. Ital. Corresp. 
Memb. Soc. Geol. de Belg. Memb. Soc. Geol. de Fr. Woodwardian Professor 
of Geology in the University of Cambridge. 18 Hills-road, Cam- 
bridge. 

t Hull, Edward, M.A. F.G.S. LL.D. (Glasc) late Director of the Geological Survey 
of Ireland, and Professor of Geology in the Royal College of Science, 
Master in Engineering (Hon. Caus. Dubl.) Hon. Mem. Acad. Sci. Arner. 
Philad. Corresp. Soc. Geol. Belg. Soc. Extr. Hon. Mem. Geol. Soc. Edin., 
Glasg., Manch. 20 Arundel- gardens, Notting-hill. W. 

f Humphry, Sir George Murray, Knt, M.D. LL.D. (Edin.) Sc.D. (Dubl.) Prof, of 
Surgery in the Univ. of Cambridge, Fellow of Kings Coll. Hon. Fellow of 
Downing Coll. Grove Lodge, Cambridge. 

* Hutchinson, Jonathan, LL.D. (Glasc. and Camb.) M.D. (Dubl.) F.R.C.S. Corr. 

Mem. Soc. Chir. Paris, Hon. Mem. Soc. Derrnat. Nov. Ebor. Formerly 
President of and Professor of Pathology and Surgery in the Royal College 
of Surgeons. 15 Cavendish-square. W. 

* Hutton, Frederick Wollaston, Captain. F.G.S. C.M.Z.S. Curator of the Canter- 

bury Museum, Christchurch, Cor. du Mus. d'Hist. Nat. Paris, Cor. Mem. 
Roy. Soc. Tas. Hon. Mem. Roy. Soc. N.S.W. Cor. Acad. Nat. Sci. Philad. 
Cor. Ornith. Yer. Wien, Cor. K. K. Geol. Reichsanst. Wien. Canterbury 
Museum, Christchurch, New Zealand. 
t Jackson, John Hughlings, M.D. Coll. Reg. Med. Soc., Consulting Physician to 
the London Hospital, o Manchester-square. W. 
Jackson, Right Hon. William Lawies. 27 Cadogan-square, S.W. ; and Allerton 
Hall, Chapel Allerton, Leeds. 

* Japp, Francis Robert, M.A. Ph.D. LL.D. (St. And.) F.I.C. F.C.S. Prof, of 
Chemistry in the University of Aberdeen. University, Aberdeen. 

Jenner, Sir William, Bart., G.C.B. M.D. D.C.L. (Oxon.) LL.D. (Cantab, et Edin.) 
Physician in Ordinary to the Queen, and to H.R.H. the Prince of Wales. 
Greenu-ood, Durley, Bishop's Wallham. 

* Jervois, Sir William Francis Drummond, Lieut.-Gen., R.E., G.C.M.G. OB. 
Merleicood, Virginia Water. 

f Johnson, Sir George, Kt. M.D. (Lond.) Coll. Reg. Med. Soc, Physician Extra- 
ordinary to the Queen, Emeritus Professor of Clinical Medicine in Kings 
College, London, and Consulting Physician to King's College Hospital. 
11 Savile-roiv. W. 
Joly, John, M.A. B.E. D.Sc. 39 Waterloo-road, Dublin. 

* Jones, John Viriamu, M.A. (Oxon.) B.Sc. (Lond.) Principal and Professor of 
Physics in the University College of South Wales and Monmouthshire. 
Fellow of University College, London. 42 Park-place, Cardiff. 

Jones, Thomas Rupert, F.G.S. Hon. Mem. Gesell. Isis, Dresden, Soc. Belg. de 
Microsc, and Soc. Geol. Hydrol. Paleeontol. Brux., Geol. Assoc. Lond.. 
Geol. Socs. Edin. and Glasg., Roy. Irish Geol. Soc, and Anthrop. Inst. 
Lond. Corresp. Mem. of the K.-K. Geolog. Eeichsanst. Wien, and Acad. 
Nat. Sci. Philad. 17 Parsons Green, Fulham. S.W. 

C 2 



20 



Date of Election. 



June 7, 1877, 



June 5, 1851. 



June 2, 1881. 

June 9, 1887. 

June 5, 1890. 

June 9, 1887 



June 


9, 


1887. 


'93-95 


June 


3, 


1875. 


'88-90 


.June 


12, 


1884. 


'94-95 


June 


7, 


1883. 




June 


3, 


1875. 


'82-83 
'88-90 
'94-95 


June 


7, 


1888. 




June 


9 


1892. 





Served on 
Council. 

'87^89 



'90-95 



C. 
R. 



R. 



R. 



R. 



FELLOWS OP THE SOCIETY. (Nov. 30, 1895.) 

Judd, John Wesley, C.B. F.G.S. Professor of Geology in the Royal College 
of Science, London, and Dean of the College, Soc. Phil. Ebor. et Sci. Nat. 
Leva. Soc. Honor, Acad. Sci. Nat. Philad. Soc. Geol. Belg. Brux. Inst. 
Imp. Geol. Vindob. Corresp. 16 Cumberland-road, Kew ; Royal College of 
Science, South Kensington ; and Athenceum Club. S.W. 

Kelvin, William Thomson. Lord, Past President — D.C.L. (Oxon) LL.D. (Camb. 
Dubl. Edin.) F.R.S.E. Hon. Mem. Inst. C.E., and Elect. Eng. Professor of 
Natural Philosophy in the University of Glasgow, and Fellow of St. Peter's 
College. Cambridge, Trust. Brit. Mus. Grand Officier of the Legion of 
Honour of France. Ord. Boruss. " Pour le Merite " Eq. Comm. Ord. of 
Leopold, Belgium, Comm. Imp. Ord. of the Rose, Brazil. Assoc. Etrang. 
Inst. Fr. (Acad. Sci.) Par.; Corresp. Mem. R. Inst. Lomb., R. Acad, dei 
Lincei ; For. Mem. Soc. Roy. Sci. Gott., Soc. Ital. delle Scienze, Soc. Reale 
di Napoli, Acad. Nat. Sci. Philad. ; Hon. Mem. Acad. Imp. Sci. Vienna, 
Acad. Nov. Lync. Rom., United Service Inst. Loud., Lit. and Phil. Soc. 
Mancb., Phil. Soc. Glasg., Roy. Irish Acad. University, Glasgow ; and 
Athenceum Club. S.W. 

Kempe, Alfred Bray, M.A. 2 Paper-buildings, Temple, E.C. ; and 23 Gilbert- 
street, Brook-street. W. 

* Kennedy, Alexander B. W., LL.D. Mem. Inst, C.E. Pres. Inst. M.E. Emeritus 
Professor of Engineering and Mechanical Technology in University College, 
London- 2 Gloucester-place, Portman-square. W. 

* Kerr, Rev. John, LL.D. Mathematical Lecturer in the Free Church Training 
College, Glasgow. 113 Hill-street, Glasgow. 

King, George, M.B. LL.D. CLE. F.L.S. Superintendent of the Royal Botanical 
Gardens,. Calcutta, and of the Government Cinchona Plantations, Darjeeling. 
Seebpore, Calcutta. 

Kingsburgh (see Macdonald). 

Kirk, Sir John, G.C.M.G. K.C.B. M.D. LL.D. F.L.S. F.R.G.S. Wavertree, 
Sevenoahs. Kent ; and Athenceum Club. S.W. 

Klein, Edward Emanuel, M.D. Lecturer on General Anatomy and Physi- 
ology in the Medical School, St. Bartholomew's Hospital. 19 Earl's Court- 
square. S.W. 

Lamb, Horace, M.A. (Cantab.) Professor of Mathematics in the Owens College, 
Manchester. Burton-road, Didsbuvy, Manchester. 

Langley, John Newport, M.A.' Fellow and Lecturer of Trinity College, 
Lecturer on Histology in the University of Cambridge. Trinity College, 
Cambridge. 

Lankester, Edwin Ray — Vice-President — M.A. (Oxon.) LL.D. (St. And.) Linacre 
Professor of Human and Comparative Anatomy in the University of Oxford, 
Fellow of Merton College, Honorary Fellow of Exeter College, Oxford; 
Hon. Mem. Camb. Phil. Soc. and Roy. Phys. Soc. Edin. ; Corr. Acad. Nat. 
Sci., Philadelphia. 2 Bradmore-road, Oxford; and Athenceum Club. S.W. 

Lapworth, Charles, LL.D. (Aberd.), F.G.S. Professor of Geology in the Mason 
Science College, Birmingham. 13 Duchess-road, Edgbaston, Birmingham. 

Larmor, Joseph, M.A. D.Sc. (Lond.) Fellow of St. John's College, Cambridge . 
late Professor of Natural Philosophy in Queen's College, Galway, and 
Fellow of the Royal University of Leland. St. John's College, Cambridge. 



FELLOWS OF THE SOCIETY. (Nov. 30, 1895.) 



21 



[ Served on 
Date of Election. Council. 



June 1, 1854. 

J ime 5, 1890. 

June 3, 1880 

June 7, 1860. 



'81-83 
'93-95 



June 12, 1879. '91-92 



June 8, 1882. 



June 3, 1869. 



'74-76 
'85-87 
'91-93 



R. 



R. 



Rm. 



June 9, 1887 

June 7, 1894 
June 6, 1867, 



June 3. 1858. '61-63 
'70-72 
'78-79 
'93-94 



'93-94 



Lawes, Sir John Bennet, Bart, D.C.L. (Oxon.) LL.D. (Eclin.) Sc.D. (Cantab.) 
F.C.S. Inst. Fr. (Acad. Sci.) Con:. Rothamsted, St. Albans. 

* Lea, Arthur Sheridan, Sc.D. Fellow, Lecturer in Physiology, and Assistant 

Tutor of Gonville and Caius College, Assistant Lecturer of Trinity 
College, and University Lecturer, Cambridge. Gonville and Cains College, 
Cambridge. 

* Limerick, Charles Graves. Lord Bishop of, D.D., D.C.L. The Palace, Limerick, 

Ireland. 

Lister, Sir Joseph, Bart.— President— F.R.C.S. D.C.L. (Oxon.) Hon. M.D. 
(Dubl. Wiirzburg, Bologna) LL.D. (Cainb. Edin. Glasg.) Emeritus 
Professor of Clinical Surgery, King's College, London, Surgeon Extraor- 
dinary to the Queen. Knt. Coram. Ord. Danebrog\ Knt. Pruss. Ord. " Pour 
le Merite." Inst. Fr. (Acad. Sci.) Mem. Assoc. Hon. Mem. Amer. Acad. Arts 
and Sci. 12 Park-crescent, Portland-place. W. 

Liveing, George Downing, M.A. Sc.D. (Dubl.) Professor of Chemistry. Fellow 



of St. John's College, Cambridge 



* Liversidge, Archibald, M.A. 



Nevmham, Cambridge. 
(Camb.) F.G.S. F.C.S. F.I.C. 



F.R.G.S., Assoc. 



R.S.M. V.P. Roy. Soc. N.S.W. Memb. Phys. Soc. Lond. Min. Soc. Gr. Brit. 
Min. Soc. Fr. Corr. Mem. Roy. Soc. Tasm. Roy. Soc. Queensland, Soc. 
d'Acclimat. Maur. Senck. Naturf. Gesell. Frankf. Hon. Mem. Roy. Soc. 
Vict. New Zeal. Inst, and K. Leop. Carol. Acad. Halle. Corresp. Edin. 
Geol. Soc. Professor of Chemistry in. the "University of Sydney. The 
University, Sydney, New South Wales. 
\ Lockyer, Joseph Norman, C.B. F.R.A.S. Phys. Soc. Loud., Ord. Imp. Bras. Rosae. 
Eq. Inst. Fr. (Acad. Sci.) Soc. pro fov. Indust. Nat. Par. Soc. Reg. Sci. 
Gott. Frank. Inst. Philad. Soc. Phys. Soc. Reg. Med. Brux. Soc. Spettros. 
Ital. Reg. Sci. Panorm. et Hist. Nat. Genev. Mem. Corr. Acad. Reg. Line. 
Romse. et Soc. Phil. Amer. Philad. Socius. Soc. Lit. et Phil. Mane. Acad. 
Gioen. Sci. Nat. Catan. Soc. Phil. Ebor. et Univ. Lehigh Soc. Honor. 16 
Penywern-road, S.W. ; Observatory House, Westgate-on-Sea ; and Royal College 
of Science, South Kensington. S.W. 

* Lodge, Oliver Joseph, D.Sc. LL.D. (St. And.) Professor ot Physics in 
University College, Liverpool. 2 Grove-park, Liverpool. 

* Love, Augustus Edward Hough, M.A. Fellow of St. John's College, Cambridge. 

St. John's College Cambridge. 
f Lowe, Edward Joseph, F.R.A.S. F.L.S. F.G.S. F.M.S. Soc. Lit. et Phil. 
Mane, et Lye. Hist. Nat. Nov. Ebor. Mem. Corr. Shirenewton Hall, near 
Chep/stow, Monmouthshire. 
Lubbock, Right Hon. Sir John, Bart., D.C.L. (Oxon.) LL.D. (Cantab., Dubl. et 
Edin.) M.D. (Wiirzb.) V.P.L.S. F.G.S. F.Z.S. F.S.A. F.E.S. Trust. Brit. Mus., 
Assoc. Acad. Roy. des Sci. Brux., Hon. Mem. Amer. Ethnol. Soc. Anthrop. 
Socc. Wash. (U.S.), Brux., Firenze., Anthrop. Verein, Graz., Soc. Entom. de 
France, Soc. Geol. de la Suisse, and Soc. H el vet. des Sci. Nat., Mem. Amer. 
Phil. Soc. Philad. Con-esp. Mem. Soc. Nat. des Sci. Nat. de Cherb., Berl. Gesell. 
fur Anthrop., Soc. Romana di Antrop., Soc. d'Emul. d' Abbeville, Soc. d'Ethn. 
de Paris, Soc. Cient. Argentina, Soc. de Geog. de Lisb., Acad. Nat. Sci. 
Philad., Numis. and Ant. Soc. Philad., For. Assoc. Mem. Soc. d' Anthrop. de 
Paris, For. Mem. Amer. Antiq. Soc. High Elms, Down, Kent. 



22 

Date of Election. 

June ~~T, 1894 
June 2, 1881 



June 13, 1895 
June 1, 18(35. 
June 3, 1880 

June 9, 18,59. 
May 3, 1888 

June 13, 1895. 
June 7, 1877. 



Served on 



'91-95 



June 12, 1884.: '92-93 



June 7, 1S77. 



June 2, 1881.! '87-89 

June 5, 1890. 

June 8, 1882. 

June 7, 1377. 

.lime 11, 1857. 
June 12. 1873. 



FELLOWS OF THE SOCIETY. (Nov. 30, 1895.) 

* Lydekker, Richard, B.A. (Camb.). The Lodge, Harpenden, Herts. 

* Macalister, Alexander, M.A. M.D. (Dubl. & Camb.) M.D. Sc.D. (Dubl.) LL.D. 

(Glasg.) Professor of Anatomy in the University of Cambridge. Torrisdale, 
Cambridge. 

* 3LClean, Frank, M.A. LL.D. (Glasg.) F.R.A.S. M. Inst. C.E. Rusthall House, 

Tunbridge Wells. 
M c Clintock, Sir Francis Leopold, Admiral, K.C.B. D.C.L. L.L.D. 8 Atherstone- 
terrace, Gloucester-road. S.W. 

* M'Coy, Sir Frederick, K.C.M.G. M.A. D.Sc. (Cantab.) F.G.S. Professor of Natural 

Sciences in the University, Melbourne, Soc. Phil. Cantab. Soc. Honor. 

Melbourne, Australia. 
f Macdonald, John Denis, M.D. Inspector-General of Hospitals and Fleets, 

R.X. 82 Messina-avenue, West Hampstead. N.W. 
f Macdonald, Right Hon. John Hay Athole, C.B. LL.D. F.R.S.E. M.I.E.E. Lord 

Justice-Clerk of Scotland, and Lord President of the Second Division of 

the Court of Session. 15 Abercromby-place, Edinburgh. 

* Mace-wen, William, M.D. (Glasg.) Hon. LL.D. (Glasg.). Professor of Surgery 

in the University of Glasgow. 3 Woodside-crescent, Glasgow. 

Mcintosh, William Carmichael, M.D. (Edin.) LL.D. (St. And.) F.L.S. F.R.S.E. 
L.R.C.S.E. C.M.Z.S. Professor of Natural History in the University of 
St. Andrews ; Director of the University Museum, and of the Marine 
Laboratory, St. Andrews; Mem. Fishery Board for Scotland; Hon. 
Mem. Psychol. Soc. Paris and Soc. Centrale d'Aquicult. de France. 
2 Abbots ford-crescent, St. Andrews, Scotland. 

* M'Kendrick, John Gray, M.D. LL.D. F.R.S.E. F.R.C.P.E. Professor of 
Physiology in the University of Glasgow. 2 Florentine-gardens, Glasgow. 

M°Lachlan, Robert, F.L.S. F.Z.S. F.E.S. Soc. Imp. Ami. Sci. Nat. Mosq. Inst. 
Nov. Zel. Soc. pro Faun, et Flo. Fenn. Soc. Entom. Batav. Soc. Entom. Belg. 
Soc. Entom. Helvet. Soc. Nat. Hist. Glasc. Soc. Honor. Soc. Reg. Sci. 
Leodii. Corresp. Westview, 23 Clarendon-road, Lewisham. S.E. 

* M c Leod, Herbert, F.I.C. F.C.S. Professor of Chemistry hi the Royal Indian 
Engineering College, Cooper's Hill. The College, Coopers-hill, Staines. 

* MacMahou, Percy Alexander, Major, R.A. Pres. Lond. Math. Soc. Artillery 
College, Woolwich ; and Regency-mansions, 40 Shaftesbury-avenue. W. 

* Malet, John Christian, M.A. Assistant Commissioner of Intermediate Education. 
Ireland. Carbery, Silchester-road, Kingstown, Co. Dublin. 

\ Mallet, John William, Ph.D. (Gott.) M.D. LL.D. F.C.S. Mem. of the Chem. Socs. 
of Paris, Berlin, and New York, and oi the Amer. Phil. Soc. Philad. Fellow 
of the Coll. Phys. Philad. and Hon. Fellow of the Med. Chir. Faculty of 
Maryland. University of Virginia, Albemarle Co., Virginia, United States. 
Marcet, William, M.D. F.C.S. Past Pres. Royal Meteorol. Soc. Floicer-meaJ, 
Wimblsdon-parh, S.W. ; mid Athenaeum Club. S.W. 

t Markkarn, Clements Robert, C.B. P.R.G.S. F.S.A. Acad. Caes. Nat. Cur. 
Socius Soc. Geog. Par. Berol. Vindob. Hist, Philad. et Univ. Chil. Soc. Honor. 
AtJiena'um Club; and 21 Ecclesfon-sguare. S.W. 



FELLOWS OF THE SOCIETY. (Nov. 30, 1895.) 



23 



Date of Election. 

June 4, 1891. 

Jane 4, 1885. 
June 13, 1895. 

June 2, 1870. 

June 2, 1870. 

June 12, 1879. 

June 7, 1877. 
June 4, 1886. 

June 1, 1876. 
June 2, 1892. 
June 4, 1874. 

•June 9, 1887. 

June 13, 1895. 
June 3, 1869. 

June 8, 1871. 
June 4, 1891. 
June 5, 1856. 
Dec 15, 1892. 
Jitne 3. 1880. 



Served on 
Council. 



'73-75 



* Marr, John Edward, M.A. F.G.S. Fellow and Lecturer of St. John's College, 

Cambridge, and University Lecturer in Geology. St. John's College, 
Cambridge. 

* Martin, Hemy Newell, M.A. (Camb.) M.B. and D.Sc. (Loud.) (Hon.) M.D. Univ. 
of Georgia. Physiological Laboratory, University, Cambridge. 

* Martin, Sidney, M.D. B.S. B.Sc. F.R.C.P. Assistant i.liysician in University 
College Hospital, and in the Hospital for Consumption, Brompton. 

10 Mansfield-street, Cavendisli-square. ~W. 
Maskelyne, Nevil Story, M.A. F.G.S. Late Professor of Mineralogy in the 
University of Oxford, Hon. Fellow Wadham Coll. Oxon. Soc. Reg. Geol. 
CumuL. Soc. Imp. Min. Petrop. et Soc. Hist. Nat. Bost. Soc, Acad. Pieg. 
Bavar. Monach. Soc. Cor. Basset Boxen House, Swindon. 
t Masters, Maxwell Tylden, M.D. M.R.C.S. F.L.S. Ord. Leopold Eques. Inst. Fr. 
(Acad. Sci.), Acad. Sci. Nat. Philad., Soc. Beg. Liege et Soc. Sci. Nat. 
Cherbourg Soc. Corr. Mount Avenue, Ealing. W. 

* Matthey, George, F.C.S. Assoc. Inst. C.E. Leg. Honor. (France), Ord. Franz 

Josef (Austria), Great Gold Medal for Arts and Science (Germany). Cheyne 
House, Chelsea Embankment. S.AY. 
| Medlicott, Henry Benedict, M.A. (Dubl.) F.G.S. Late Director (1876-87) of 
the Geol. Survey of India. 43 St. Johns-road, Clifton, Bristol. 

* Meldola, Raphael, For. Sec. C.S. F.I.C. F.R.A.S. F.E.S. Professor of Chemistry 

in the Finsbury Technical College, City and Guilds of London Institute. 
6 Brunswick-square. AV.C. 
t Meldrum, Charles, C.M.G M.A. LL.D. F.R.A.S. F.R, Met. Soc. Director of the 
Royal Alfred Observatory, Mauritius. Mauritius. 

* Miall, Louis Compton, F.L.S. F.G.S. Professor of Biology in the Yorkshire 

College, Leeds. Crag Foot, Ben Rhydding, Leeds. 
Mills, Edmund James, D.Sc. F.C.S. F.I.C. Young Professor of Technical 

Chemistry in the Glasgow and West of Scotland Technical College, 

Glasgow. 60 John-street, Glasgow. 
Milne, John, F.G.S. Assoc, and Hon. Fellow of King's College, London, Late 

Professor of Mining and Geology in the Imperial College of Engineering, 

Japan. Shide Hid JIousc, Shide, Neuport, Isle of Wight. 

* Minchin, George M., M.A. (Dubl.). Professor of Mathematics in the Royal 

Indian Engineering College, Cooper's-hill. The College, Cooper s-hill, Staines. 
Mivart, St. George, Ph.D. M.D. F.L.S. F.Z.S. Acad. Sci. Philad. Corr. 

Mem. Professor of the Philosophy of Biology in the University of 

Louvain. 15 Duke-street, St. James's. S.W. 
Moncrieff, Sir Alexander, Colonel (late R.A.), K.C.B. 15 Vicarage-gate, Ken- 
sington, W. ; and Athenaium Club. S.W. 
Mond, Ludwig, Ph.D. F.I.C. F.C.S. The Poplars, 20 Avenue-road, Regents-park, 

N.W. ; and Wilmington Hall, Northwich. 
t Moore, John Carrick, M.A. F.G.S. 113 Eaton-square, S.W. ; and CorswalL 

Stranraer, Wigton slave. 
t Morley, Right Hon. John, M.A. (Oxon.) Hon. LL.D. (Camb. and Glasg.) 95 

Elm Park Gardens; and, Athenaeum Club. S.W. 

* Moulton. John Fletcher, M.A. Q.C. 57 Onslow-square. S.W. 



24 



Date of Election. 



June (3, 1861 



June 7, 1866, 



Mar. 9, 1882. 

Jane 3, L875 
June 2, 1870. 



June 1. 1893. 

June 3, 1880, 

June 8, 1882, 

June 2, 1870, 



June 5, 1890. 

Jan. 8, 1880. 

June 9, 1859 

June 4, 1863 

June 4, 1868, 

June 7, 1855. 

June 4, 1885. 

June 5, 1851. 

June 8, 1882.: 



Served on 
Council. 



'83-85 
'89-91 



'79-81 
'89-91 



92-94 



'81-85 
'89-90 



'64-66 
'79-81 



'75-76 
'80-82 



'51-.>6 
'60-62 
'71-72 
'79-81 

\SS ,S>) 



R. 



R. 



R. 



FELLOWS OF THE SOCIETY. (Nov. 30, 1895.) 

Mueller, Baron Ferdinand von, K.C.M.G. M.D. Ph.D. Hon. LL.D. (Univ. 

McGill) F.L.S. F.OS. F.G-S. F.RG.S. C.M.Z.S. Corr. Mem. Geol. Soc. 

Eclin., Bot. Soc. Lond. and Edin., and Piiarm. Soc. Lond. Hon. Mem. 

Soc. of Arts, Roy. Hort. Soc, Roy. Irish Acad., Roy. Hist. Soc, Inst. 

Egypt, Inst. Nat. Genevois, R. Scott. Geogr. Soc. and Geogr. Soc. Manch. 

For. Mem. of the Academies of Stockholm, Copenhagen, Boston, Munich, 

and Halle. Corr. Mem. K. Gesell. der Wiss. Gottingen. Pres. Roy. 

Geogr. Soc. Austr. (Vict. Branch), Government Botanist, and Director of 

the Botanic Museum, Melbourne. Melbourne, Victoria. 
Miiller, Hugo, Ph.D. LL.D. (St. And.) V.P.C.S. Ord. SS rura Lazar. et Maurit. 

Eq. 13 Park-square, N.W. ; Crosby-hill, Camberley, Surrey ; and Athenaeum 

Club. S.W. 
Mundella, Right Hon. Anthony John. 16 Eloaston-place ; and Athenceum and 

Reform Clubs. S.W. 
\ Nares, Sir George Strong, Vice-Admiral, K.C.B. 1 Beaufort-villas, Surbiton. 
Newton, Alfred, M.A. F.L.S. V.P.Z.S. Professor of Zoology and Comparative 

Anatomy in the University of Cambridge. Magdalene College^ Cam- 
bridge. 

* Newton, Edwin Tulley, F.G.S. F.Z.S. Geological Museum, Jermyn-street. S.W. 
Niven, Charles, M.A. F.R.A.S., Professor of Natural Philosophy in the University, 

Aberdeen. 6 Chanonry, Old Aberdeen. 
Niven, William Davidson, M.A., Director of Studies in the Royal Naval College, 

Greenwich. Greenwich. S.E. 
Noble, Sir Andrew, Capt.. K.C.B. F.R.A.S. F.C.S. Ord. Ccron. Ital. et Ord. 

Jes. Christ Portog. Com.. Ord. Imp. Bras. Rosae Gr. Off. et Ord. Car. III. 

Hisp. Eq. Jesmpnd Dene House, Newcastle-upon-Tyne; and AtJienceum 

Club. S.W. 

* Norman. Rev. Alfred Merle, M.A. D.C.L. F.L.S. Hon. Canon of Durham. 
Bummoor Rectory, Fence Houses, Co. Durham. 

f Northbrook, Thomas George Baring, Earl of, LL.D. D.C.L. G.C.S.I. 4 Hamilton- 
place, W. : and Stratton, Micheldever Station, Hants. 

f Gelling, William. M.B. Coll. Reg. Med. Socius. V.P.C.S. Hon. Math. Phys. Doct. 
(Lugd. Bat.) Waynflete Professor of Chemistry in the University of Oxford. 
Museum ; and 15 Norham-gardetis, Oxford. 
Oliver, Daniel. LL.D. (Aberd.) F.L.S. late Keeper of the Herbarium and Library 
Royal Gardens, Kew, Emeritus Professor of Botany, University College, 
London. 10 Kew Gardens-road, Keiu. 
Ommanney, Sir Erasmus. Admiral, Knt,, C.B. LL.D. (Univ. McGill) F.R.A.S. 
F.R.G.S. Cross of Grand Coram, of Royal Ord. of the Saviour, Greece. 29 
Connaught-square, Hyde Park, W. : and United Service Club- 

f Osier, Abraham Follett. South Bank, Edgbaston, Birmingham. 

* O'Sullivan, Cornelius, F.I.C. F.C.S. 140 High-street, Burton-on- Trent. 

t Paget, Sir James, Bart., D.C.L. (Oxon.) LL.D. (Cantab, et Edin.) Hon. M.D. 
(Dubl.) Corr. Mem. Inst. Fr. (Acad. Sci.) Late Vice-Chancellor of the 
University of London, Serjeant-Surgeon to the Queen, Surgeon in Ordinary 
to H.R.H. the Prince of Wales. 5 Park-square West, Regent's Park. N.W. 
Palgrave, Robert Harry Inglis, F.S.S. Belton, Great Yarmouth. 



FELLOWS OF THE SOCIETY. (Nov. 30, 1895.) 



25 



Date of Election. 

June 7, 18S8. 


Served on 
Council. 


June 2, 1870. 




June 4, 1863. 





'92-94 



June 2, 1892. 

June 2, 1892. 

June 7, 1894. 

Juue 7, 1866. 

June 5, 1890. 

June 4, 1885. 

June 4, 1868. 

June 9, 1887 

June 5, 1890 

April 4, 1889. 

June 1, 1876. 



June 9, 1848.1 '56-58 
'74-76 

'86-87 



June 6, 1861. 
June 6, 1889. 

June 13, 1895. 
June 7, 1888. 



'63-65 

'75-77 
'87-89 



'94-95 



i). 

R. 



* Parker, T. Jeffery, D.Sc. (Lond.), A.R.S.M. A.L.S. C.M.Z.S. F.R.M.S. Mem. 

Imp. Soc. Nat. Moscow, Corr. Mem. Linn. Soc. N.S.W. Professor of 
Biology at the University of Otago. Dunedin, New Zealand. 
f Parsons, R. Mann, Major-General R.E. Hyde-vale, Blackheath. S.E. 
t Pavy, Frederick William, M.D. (Lond.) LL.D. (Glasc.) Coll. Reg. Med. Socius, 
Consulting Physician and formerly Lecturer on Physiology and Comparative 
Anatomy and Zoology, and on Medicine, at Guy's Hospital. 35 Grosvenor- 
street. W. 

Peach, Benjamin Neeve, F.R.S.E. F.G.S. Geological Survey Office, Sheriff Court- 
buildings, Edinburgh. 

Pedler, Alexander, F.C.S. F.I.C. Fellow of the University of Calcutta; 
Professor of Chemistry, Presidency College, Calcutta ; and Meteorological 
Reporter to the Government of Bengal. Presidency College, Calcutta. 

Penrose, Francis Crannier, M.A. F.R.A.S. Honorary Fellow of Magdalene 
College, Cambridge. Colebyfield, Copse Hill, Wimbledon. S.W. 

Perkin, William Henry, V.P.C.S. LL.D. (St. And.) Ph.D. Tlie Chestnuts, Sudbury, 
Harrow. 

Perkin, William Henry, junior, Ph.D. F.R.S.E. F.I.C. F.C.S. Professor of 
Organic Chemistry in Owens College, Manchester. Fairview, Wilbraham- 
road, Fallowjield, Manchester. 

* Perry, John, D.Sc. Professor of Mechanical Engineering and Applied Mathematics 
in the City and Guilds of London Technical College, Finsbury. 31 Brunsivick- 
square. W.C. 

Pettigrew, James Bell, M.D. and F.R.C.P. (Edin.), LL.D. (Glasg.) Professor of 
Medicine and Anatomy and Dean of the Medical Faculty in the University 
of St. Andrews ; Laureate Inst. Fr. St. Andrews. N.B. 

Pickard-Cambridge, Rev. Octavius, M.A. Bloxworth, Wareham, Dorset. 

* Pickering, Spencer Percival Umfreville, M.A. F.C.S. F.I.C. Mem. Phys. Soc. 
Lond. Deutsch. Chem. Gesell. Berlin. Harpenden, Herts. 

f Pi-bright, Right Hon. Baron Henry de Worms, Lord. 42 Grosvenor-place, S.W. ; 

Henley-park, Guildford. 
\ Pitt-Rivers, Augustus Henry Lane-Fox, Lieut.-General, D.C.L. (Oxon.) V.P. 

Anthrop. Inst. F.S.A. F.G.S. 4 Grosvenor-gardens, S.W. ; and Rushmore, 

Salisbury. 
■ Playfair (of St. Andrew's), Right Hon. Lyon, Lord, G.C.B. LL.D. Ph.D. V.P.C.S. 

& R.S.E. Comm. Leg. Honor, and of Ord. Fran. Joseph Austr., Stell. Bor. Suec. 

Eq. 68 Onslow-gardens. S.W. 
Pole, William, Mus. Doc. Oxon., Knt. Commander, Imp. Ord. of the Rising Sun, 

Japan. Mem. and Hon. Sec. Inst. C.E. Soc. Reg. Edin. Soc. Atlienamm Club. 

S.W. 

* Poulton, Edward Bagnall, M.A. (Oxon.) F.L.S. F.Z.S. F.G.S. Hope Professor 
of Zoology in the University of Oxford. Wykeham House, Banbury-road, 
Oxford; and St. Helen's Cottage, St. Helen's, Isle of Wight. 

* Power, William Henry, Assistant Medical Officer, Local Government Board. 
Glenbrook, Greenhithe ; and Local Government Board, Whitehall. S.W. 
Poynting, John Henry, D.Sc. Professor of Physics at the Mason College. 
Birmingham. Foxhill, Alvechurch, Worcestershire. 

D 



26 



! Served on 
Date of Election. Council, 



June 2, 1881. 



June 2, 1853 



June 3, 


1852. 


'56-58 
'64-65 
75-77 
'85-87 
'92-93 


June 13, 


1895. 




June 4, 


1886. 


91-92 


June 8, 


1871. 





June 7, 1888. 

June 2, 1870. 
June 12, 1884 

June 12, 1873. 



87-89 



'60-62 
'68- 69 
72-74 
'82-84 



77-79 
'84-95 



June 1, 1876. 

June 7, 1883 

June 3, 1880 

June 3, L869 



R. 



D. 



R. 



FELLOWS OF THE SOCIETY. (Nov. 30, 1895.) 

* Preece, William Henry, C.B. Fellow of King's College, London, M. Inst. Electr. 

Eng. Mem. Inst. C.E. Hon. Mem. Inst. E.E. (America) Officier Leg. Honor, 
France. Telegraph Department, General Post Office; and Gothic Lodge, 
Wimbledon. 
t Prestwich, Joseph, D.C.L. (Oxon.) F.G.S. F.C.S. Assoc. Inst. C.E. Inst. Fr. 
(Acad. Sci.) Corresp. Soc. Geol. Fr. Socius. Inst. Imp. Geol. Vindob. Acad. 
Lync. Romas. Acad. Reg. Sci. Belg. Soc. Anthrop. Brux. Soc. Phil. Amer. 
Philad. Pont. Acad. Romse. Sci. Nat. Helvet. Soc. Vaud. Hist. Nat. et Soc. 
Lit. Phil. Mane. Soc. Honor. Soc. Reg. Geol. Cornub. Soc. Hist. Nat. Bost. 
Mem. Corr. Darent-Hulme, Shoreham, Sevenoaks. 
Price, Rev. Bartholomew, D.D. F.R.A.S., Master of Pemb. Coll., Sedleian Prof. 
• of Nat. Phil., and Hon. Fellow of Queen's College, Oxford. Canon of 
Gloucester. Masters Lodge, Pembroke College, Oxford; and Athenaum Club. 
S.W. 

* Purdie, Thomas, B.Sc. Ph.D. A.R.S.M. Professor of Chemistry in the University 
of St. Andrews. The University, St. Andrews. 

Pye-Smith, Philip Henry, M.D. B.A. F.R.C.P. Physician to Guy's Hospital, 
late Lect. on Physiol, at Guy's Hospital. 48 Brook-street. W. 

Quain, Sir Richard, Bart., M.D. (Lond.) Hon. M.D. (Dubl. and Roy. Univ. 
Irel.) Hon. LL.D. (Edin.) F.R.C.P. Hon. F.R.C.P. Irel. President of the 
General Medical Council, Physician Extraordinary to the Queen, Fellow of 
the University of London. 67 Harley-street, W. ; and Athenaeum and Union 
Clubs. S.W. 

Ramsay, William Ph.D. (Tub.) F.C.S. F.I.C. Professor of Chemistry in University 
College, London. Corresp. Inst. Fr. (Acad. Sci.). 12 Arundel-gardens, 
Notting-hill. W. 

Ransom, William Henry, M.D. Coll. Reg. Med. Soc. Consulting Physician to 
the General Hospital. Nottingham. The Pavement, Nottingham. 

Ransome, Arthur, M.A. M.D. Professor of Public Health in Owens College. 
Examiner in Sanitary Science in Cambridge and Victoria Universities. 
Sunninghurst, Lean-park, Bournemouth. 

Rayleigh, John William Strutt, Lord— Secretary — M.A. D.C.L. (Oxon.) Sc.D. 
(Camb. and Dubl.) LL.D. (Edin. Glasg. and Univ. McGill) Ph.D. (Heidel.) 
Hon. Fellow of Trinity College, Cambridge, Hon. Mem. Inst. C.E. F.R.A.S. 
Soc. Reg. Edin. Soc. Lit. et Phil. Mane. Acad. Reg. Sci. Monach. Soc. Honor., 
Inst. Fr. (Acad. Sci.). Par. Corresp., Soc. Reg. Sci. Gott. Corr; Soc, Professor 
of Natural Philosophy in the Royal Institution. Terling Place, Witharn, 
Essex. 
\ Reed, Sir Edward James, K.C.B. Broadway-chambers, Westminster. S.W. 

Reinold, Arnold William, M.A. Professor of Physics in the Royal Naval College, 
Greenwich. 28 Belmont Hill, Lee. S.E. 

Reynolds, J. Emerson, M.D. Sc.D. (Dubl.) M.R.IA. F.C.S. Professor of 
Chemistry, University of Dublin. 70 Morehampton-roa,d, Dublin. 

Reynolds, Sir John Russell, Bart., M.D. Pres. R.C.P. Emeritus Professor of 
Medicine in University College. London, Acad. Caes. Leop. et Soc. 
Neurol. Nov. Ebor. Socius. Soc. Psychol. Physiol. Par. Soc. Corresp., 
Physician in Ordinary to Her Majesty's Household. 38 Grosvenor-street. W. 



FELLOWS OF THE SOCIETY. (Nov. 30, 1895.) 



27 



Date of Election, 

June 7, 1877 



Served on 
Council. 

'82^84 



June 7, 1866. '68-70 
'72-74 
'76-78 
'86-88 



June 6, 1867. 



Jan. 13, 1842. 
June 4, 1885. 
May 24. 1860. 

June 5, 1890. 
June 6, 1878. 

June 7, 1877. 

June 3, 1875. 

June 4, 1863. 



'90-91 
'90-92 



"72-73 
'81-83 
'88-90 



June 10, 1886. 
Dec. 19, 1867. 
June 6, 1872. 

June 12, 1884. 



'71-72 

'87-88 

'88-90 



R. 



R. 



Reynolds, Osborne, M.A. (Cantab.) LL.D. (Glasgow), Mem. Inst. C.E. Hon. Fellow, 
Queen's Coll. Camb. Professor of Engineering in Owens College, Victoria 
University, Manchester. 23 Lady Bam-road, Fallowjield, Manchester. 

Richards, Sir George Henry, Admiral, K.C.B., F.R.G.S. Inst. Fr. (Acad. Sci.) 
Par. Corresp. Soc. Geog. Berol. et Soc. Geog. Ital. Flor. Inst. Nov. Zel. 
Soc. Honor. The Cottage, Fetcham, Leatherhead ; and Athenceum Club. 

s.w. 

\ Richardson, Sir Benjamin Ward, M.D. LL.D. M.A. F.S.A. Coll. Reg. Med. Soc. 
Honorary Physician to the Royal Literary Fund. Mem. Acad. Caes. Leop. 
Nat. Cur. Dresd.; Amer. Phil. Soc. Philad.; Acad. Phys. Med. Stat. Milan ; 
Phil. Soc. St. And. Soc. Ital. d'Hygiene, and Soc. Franc. d'Hygiene. 25 
Manchester-square. W. 

Riddell, Charles James Buchanan, Major-Gen. C.B. Oaklands, Chudleigh, 
Devonshire. 
* Ringer, Sydney, M.D. (Lond.) Holme Professor of Clinical Medicine, University 

College, London. 15 Cavendish-place. W. 
f Ripon, George Frederick Samuel Robinson, Marquis of, K.G. G. C.S.I. CLE. 
D.C.L. (Oxon.) F.L.S. F.R.G.S. 9 Chelsea Embankment, S.W.; and Studley 
Royal, Ripon, Yorkshire. 

Roberts, Isaac, Sc.D. (Dubl.) F.R.A.S. F.G.S. Starfield, Crowborough, Sussex. 
\ Roberts, Samuel, M.A. (Lond.). 34 Lady Margaret-road, St. John's College Park. 
N.W. 

Roberts, Sir William, B.A. M.D. (Lond.) Coll. Reg. Med. Soc. 8 Manchester- 
square. W. 

Roberts-Austen, William Chandler, C.B. F.C.S.. Prof, of Metallurgy, Royal 
College of Science, Chemist of the Royal Mint, Chev. Leg. Hon. France, 
Mem. Chem. Soc. Berlin. Royal Mint, Tower-hill, E. ; Chilworth, Guildford ; 
and Athenaeum Club. S.W. 

Roscoe, Sir Henry Enfield, Knt,, B.A. D.C.L. (Oxon.) LL.D. (Cantab, et 
Dubl. et Montr.) Hon. M.D. (Heidelb.) Ph.D. V.P.C.S. Officier Leg. Hon. 
France, Inst. Fr. (Acad. Sci.) Fellow of Univ. of Lond., Univ. Coll., and 
Eton College, Emeritus Professor of Chemistry in Victoria University 
(Owens College), Vice-President of Literary and Phil. Soc. Manchester, 
For. Mem. Acad. Sci. Paris. Hon. Mem. of the New York Acad. Sci. Berlin 
Chem. Soc. of the Verein fur Naturwiss. Brunswick, and of the Physikal. 
Verein, Frankfort-on-Main, Acad. Sci. Monach. Acad. Reg. Sci. Gott. et Soc. 
Sci. Catan. Corresp. Acad. Cses. Leop. Soc. Reg. Physiogr. Lund. Soc. 10 
Bramham-gardens, South Kensington, S.W. ; and Athenaeum Club. 

Kosebery, Right Hon. Archibald Philip Primrose, Earl of, K.G. D.C.L. 38 
Berkeley-square, W. ; and Dalmeny Bark, Linlithgowshire. 

Rosse, Laurence Parsons, Earl of, K.P. B.A. D.C.L. (Oxon.) LL.D. (Dubl.) F.R.A.S. 
Chancellor of the University of Dublin. Birr Castle, Parsonstorcn, Ireland. 

Routh, Edward John, D.Sc. (Cantab, et Dubl.) LL.D. (Glasc.) M.A. (Lond.) 
Fellow of the University of London, Hon. Fellow St. Peter's College, 
Cambridge, F.R.A.S. F.G.S. Newnham Cottage, Queen's-road, Cambridge. 

Roy, Charles Smart, M.D. (Edin.) Professor of Pathology in the University of 

Cambridge. Trinity College, Cambridge. 

D 2 



28 



Date of Election. 



June 12, 1884 



'85-86 



June 4, 1886. 

June 6, 1872. 

June 1, 1876. 
Jan. 28, 1869. 

June 4, 1863. 
June 4, 1863. 



June 12, 1873.| '82-81 
'94-95 

'87-88 



Served on 
Council. 

'87~S9 
'94-95 



'69-70 
'82-83 
'92-94 



June 2, 1881. 

June 6, 1867. 

June 6, 1878. 

June 6, 1850. 
June 12, 1879. 

June 6, 1861. 

June 7, 1894. 

June 2, 1870 



'73-75 
'84-86 
'93-95 



'90-92 



'85-87 

'72-73 

'86-87 



R. 



C. 
R. 



R. 



R. 



FELLOWS OF THE SOCIETY. (Nov. 30, 1895.) 

* Riicker, Arthur AVilliam, M.A. (Oxon.) D.Sc. (Vict.) Professor of Physics, Royal 
College of Science, London, Hon. Fellow of Brasenose Coll. Oxford, Fellow 
of the University of London, Treasurer, British Association, Corr. Mem. 
Leeds Lit. and Phil. Soc. Hon. Mem. Royal Cornwall Polytechnique Society. 
19 Gledhow-gardens, South Kensington, S.W. ; and Athenceum Club. S.W. 

* Russell, Henry Chamherlaine, C.M.G. B.A. (Sydn.) F.R.A.S. F.R. Met. Soc. 
Government Astronomer of New South Wales. The Observatory, Sydney, 
N.S. Wales. 

f Russell, William James, Ph.D. V.P.C.S. Lecturer on Chemistry at the Medical 

School of St. Bartholomew's Hospital. 34 Upper Hamilton-terrace. 

N.W. 
f Rutherford, William, M.D. F.R.S.E. Professor of Physiology in the Univ. of 

Edinburgh. The University ; and 14 Douglas-crescent, Edinburgh. 
\ Salisbury, The Most Hon. Robert Arthur Talbot Gascoigne-Cecil, Marquis of, 

E.G. M.A. D.C.L. (Oxon.) Chancellor of the University of Oxford. 20 

Arlington-street, S.W. ; and Hatfield House, Hatfield, Herts. 
Salmon, Rev. George, D.D. (Dubl. et Edin.) D.C.L. (Oxon.) LL.D. (Cantab. 

Provost of Trin. Coll. Dubl. Inst. Fr. (Acad. Sci.) Paris, Acad. Imp. Sci. 

Berol. Soc. Reg. Sci. Gott. Corresp. Soc. Reg. Sci. Hafn. Soc. Extr. Trinity 

Collegi; Dublin. 
Salter, Samuel James Augustus, M.B. London, Hon. Fellow King's College, 

London, F.L.S. Athenaeum Club; and Basingfield, near Basingstoke, Hants. 
Salvin, Osbert, M.A. F.L.S. F.Z.S. Hawksfold, Femhurst, Haslemere. 

* Samuelson, Right. Hon. Sir Bernhard, Bart. Mem. Inst. C.E. 56 Princes-gate. 
S.W. 

Sanderson, J. S. Burdon, M.A. (Oxon.) M.D. LL.D. Sc.D. (Dubl.) LL.D. 
(Edin.) D.C.L. (Dunelm.) F.R.S.E. F.R.C.P. Regius Professor of Medicine 
in the University of Oxford, Hon. Fellow of Magdalen College. Physio- 
logical Laboratory ; and 64 Banbury-road, Oxford. 

\ Schafer, Edward Albert, M.R.C.S. Jodrell Professor of Physiology, University 
College, London. Croxley Green, Rickmansworth. 

t Schunck, Edward, F.C.S. Kersal, Manchester. 

* Schuster, Arthur, Ph.D. F.R.A.S. Professor of Physics in Owens College, 

Victoria University, Manchester. 4 Anson-road, Victoria-park, Manchester. 
Sclater, Philip Lutley, M.A. Ph.D. (Bonn) Hon. Fellow of Corpus Christi 
College. F.L.S. F.G.S. F.R.G.S. Secretary of the Zoological Society 
of London. 3 Hanover-square, W. ; and Odiham Priory, WincMeld, 
Hants. 

* Scott, Dukinfield Henry, M.A. (Oxon.) Ph. D. (Wiirzb.) F.L.S. F.G.S. Honorary 

Keeper of the Jodrell Laboratory, Royal Gardens, Kew. Old Palace, 
Richmond, Surrey. 
t Scott, Robert Henry, M.A. F.R. Met. Soc. Secretary to the Meteorological 
Council. Ord. Coron. Ferr. Austr. Eq. Acad. Cass. Leop. Soc, Soc. Met. 
Fr. Par. Soc. Imp. Reg. Zool. Bot. Soc. Met. Austr. Vindob. Soc. Met. 
Germ. Berol. et Soc. Nat. Scrutat. Emb. Soc. Honor. Inst. Geol. Imp. 
Vindob. et Soc. Isis Dresd. Mem. Corr. Meteorological Ojfice, 63 Victoria- 
street ; and 6 Elm-park-gardens. S.W. 



FELLOWS OF THE SOCIETY. (Nov. 30, 1895.) 



29 



Date of Election. 

June 4, 1886 
June 12, 1879 



June 4, 1874. 

June 5, 1890. 

May 7, 1840. 

June 4, 1891. 

June 1, 1893. 

Jan. 9, 1845. 

June 5, 1862. 

June 7, 1894. 

June 9, 1887. 

June 6, 1889. 

June 11, 1857. 

June 6, 1878. 

June 1, 1893. 



Served on 
Council. 

'92^94 



'69-70 
'78-80 



'76-77 



R. 



* Sedgwick, Adam, M.A. Fellow and Lecturer of Trin. Coll., Cambridge, and 

Header of Animal Morphology in the University. Wlvitefield, Great Skelford, 
Cambridge. 

* Seeley, Harry Govier, F.L.S. F.G.S. F.Z.S. F.R.G.S. Professor of 
Geography and Lecturer on Geology in King's College, London, Inst. 
Imp. Keg. Geol. Vindob. et Acad. Sci. Nat. Philad. Corresp. Soc. Phil. 
Ebor. Soc. Imp. Sci. Nat. Hist. Mosq. Soc. 25 Palace-gardens-terrace, 
Kensington. W. 

Selwyn, Alfred Richard Cecil, C.M.G. F.G.S. Late Director of the Geological 
Survey of Canada. Sussex-street, Ottawa, Canada. 

* Sharp, David, M.B. CM. (Edin.) Hon. M.A. (Camb.) F.L.S. F.Z.S. Hon. Mem. 
New Zealand Inst. Museum of Zoology, Cambridge ; and Hawthorndene, 
Hills-road, Cambridge. 

t Sharp, William, M.D. F.G.S. Horton House, Rugby. 

Shaw, William Napier, M.A. Fellow and Senior Tutor of Emmanuel 
College, Cambridge. Emmanuel College, Cambridge. 

* Sherrington, Charles Scott, MA. M.D. (Camb.) Professor of Physiology in 
University College, Liverpool. 16 Grove-road, Liverpool. 

Simon, Sir John, K.C.B. F.R.C.S. D.C.L. (Oxon.) LL.D. (Cantab, et Edin.) M.D. 
(Dubl). M.Chir.D. (Munich), Consulting Surgeon to St. Thomas's Hospital. 
40 Kensington-square. W. 

Simpson, Maxwell, B.A. M.B. M.D. & LL.D. (Hon. Dubl.) F.C.S. D.Sc. F.I.C. Hon. 
F.K.Q.C.P. (Dubl.) Late Professor of Chemistry in Queen's College, Cork. 
Late Fellow of the Royal University of Ireland, 9 Barton-street, West Ken- 
sington. W. 

* Smith, Rev. Frederick John, M.A. (Oxon.) University Lecturer in Mechanics and 
Millard Lecturer in Experimental Mechanics, Trinity College, Oxford. 28 
Norham-gardens, Oxford. 

* Snelus, George James, F.C.S. A.R.S.M. Mem. Inst. M.E. Vice-Pres. Iron and 
Steel Inst. Ennerdale Hall, Frizington, Cumberland.. 

* Sollas, William Johnson, D.Sc. (Camb.) LL.D. (Dubl.) F.R.S.E. F.G.S. Pro- 
fessor of Geology in the University of Dublin. Lisnabin, Dartry-park-road, 
Rathgar, Dublin. 

Sorby, Henry Clifton, LL.D. (Cantab.) F.L.S. F.G.S. F.Z.S. F.S.A. F.R.M.S. 
Soc. Min. Petrop. Soc. Holland. Harl. Socius., Acad. Lync. Romas. Adsoc. 
Extr., Amer. Acad. Arts et Sci. Soc. Honor. Acad. Sci. Nat. Philad. et Lye. 
Hist. Nat. Nov. Ebor. Corr. Mem. Broomfield, Sheffield. 
t Sprengel, Hermann Johann Philipp, Ph.D. (Heidelb.) F.C.S. Royal Prussian 
Professor (titular). Savile Club, 107 Piccadilly. W. 

* Stirling, Edward Charles, C.M.G. M.A. M.D. (Camb.) F.R.C.S. C.M.Z.S. Senior 

Surgeon, Adelaide Hospital ; Lecturer on Physiology in the University of 
Adelaide ; Hon. Director of the South Australian Museum. The University, 
Adelaide, South Australia. 



30 

Date of Election. 

June ~5, 1851. 



June 4, 1868. 

June 2, 1881. 
June 6, 1861. 
June 1, 1854 

Mar. 22, 1888, 
June 7, 1894. 
Apr. 25, 1839. 



Served on 
Council. 

'54^92 



C. 

Rm. 



'81-83 



'72-74 
'80-81 
'84^S6 
'90-91 



'62-64 
'84-85 



June 


6, 


1878. 


June 


7, 


1888. 


June 


5, 


1890. 


June 


3, 


1869. 



c. 

R. 



FELLOWS OF THE SOCIETY. (Nov. 30, 1895.) 

Stokes. Sir George Gabriel, Bart. — Past President — M.A.. D.C.L. (Oxon.) 
LL.D. (Dubl. Edin. et Cant.) D.Sc. Lucasian Professor of Mathematics 
in the University of Cambridge, F.C.P.S. F.R.S.E., Hon. Memb. Inst. C.E., 
Soc. Reg. Hib. Lit. et Phil. Mane, et Med. Chi. Lond. Soc. Honor. 
Ord. Boruss. "Powr le MSrite" Eq. Acad. Imp. Sci, Vindob. Inst. Fr. 
(Acad. Sci.) Par. Acad. Sci. Berol. Soc. Reg. Sci. Gott. Corresp. Soc. 
Gall. Phys. Reg. Sci. Upsal. Acad. Sci. Bavar. et Acad. Nov. Lync. Rom. 
Soc. Extr. Soc. Phil. Amer. et Soc. Batav. Roterod. Socius et Acad. Amer. 
Bost. Soc. Philos. Glasc. et Mach. Civ. Inst, et Soc. Asiat. Beng. Soc. Honor. 
Lens field Cottage, Cambridge; and Athenceum Club. S.W. 

t Stone, Edward James, M.A. F.R.A.S. Radcliffe Observer., Ph.D. (Padua) Hon. 
Fellow Queen's Coll. Camb., Hon. Mem Lit. Phil. Soc. Mane. Corresp. 
Mem. Soc. Nat. Sci. Nat. Cherbourg. Radcliffe Observatory, Oxford; and 
Athenaeum Club. S.W. 

* Stoney, Bindon Blood, LL.D. M. Inst. C.E. M.R.I.A. M.I.N.A. 14 Elgin-road, 
Lublin. 

\ Stoney, George Johnstone, M.A. D.Sc. Vice-President R.D.S. F.R.A.S. 8 
Upper Hornsey-rise. N. 

f Strachey, Richard, Lieut.-General, RE. C.S.I. LL.D. (Cantab.) V.P.R.G.S. 
F.G.S. F.L.S, Chairman Meteorological Council. 69 Lancaster-gate, Hyde- 
park. W . 

Sudeley, Charles Douglas Richard Hanbury-Tracy, Lord. Ormeley Lodge, Ham 
Common, Surrey. 

* Swan, Joseph Wilson, M.A. (Durh.) F.C.S. F.I.C. M. Inst. Elec. Eng. 58 
Holland-park. W. 

\ Sylvester, James Joseph, M.A. D.C.L. (Oxon.) Hon. Sc.D. (Camb.) LL.D. 
(Dubl. et Edin.) F.R.S.E. Hon. Fellow of St. John's Coll. Camb. and 
Fellow of New Coll. Oxford, Savilian Professor of Geometry in the 
University of Oxford, Officer of the Legion of Honour, Inst. Fr. (Acad. Sci.) 
et Soc. Philom. Par. Acad. Imp. Sci. Petrop. Reg. Sci. Berol. 1st. Lomb. 
Mediol. Soc. Sci. Nat. Carob. et Soc. Philom. Par. Mem. Corr. Acad. 
Reg. Sci. Roma?. Acad. Imp. Sci. Vindob. Soc. Reg. Sci. Gott. Reg. Sci. 
Neapol. Acad. Sci. Amer. Bost. et Acad. Nat. Sci. Wash, et Philad. et Soc. 
Ital. Sci. Adsoc. Extr. Soc. Reg. Edin. Acad. Reg. Hib. Lit. Phil. Mane, et 
Univ. Kasan Soc. Honor. Athenmum Club, S.W. ; and New College, 
Oxford. 

t Symons, George James, Sec. Roy. Met. Soc, Mem. of the Scot. Met. and 
Soc. Met. de Fr., Corresp. Mem. of the Deutsche Met. Gesell. and of the 
Soc. Reg. de Med. Pub. de Belg., Registrar of the Sanitary Institute, 
Chev. de la Legion d'Honneur. 62 Camden-square. N.W. 

* Teale, Thomas Pridgin, M.A. F.R.C.S. 38 Cookridge-street, Leeds. 

* Teall, J. J. H., M.A. F.G.S. 2 Sussex-gardens, West Dulwich, S.E. ; and 

Geological Museum, Jermyn-street. S.W. 
Tennant, James Francis, Lieut.-General, R.E. CLE. V.P.R.A.S. 11 Clifton- 
gardens, Maida-hill. W. 



FELLOWS OF THE SOCIETY. (Nov. 30, 1895.) 



31 



Date of Election. 

June 4, 1891. 



Served on 
Council. 



June 12, 1884. '89-91 



June 5, 1890. 



June 1, 1893. 

June 1, 1876. '90-91 
'93-95 



June 3, 1869. 

June 3, 1880. '92-94 

June 4, 1891 

June 6, 1889 



June 6, 1878. 

June 6, 1867. 

June 6, 1889. 

June 1, 1893. 

June 2, 1881. 



June 7, 1888 
June 7, 1883. 

June 4, 1868 



R. 



R. 



* Thompson, Silvanus Phillips, B.A. D.Sc. (Lond.), F.R.A.S. M.D. (Regiomont), 
Reg. Acad. Sci. Suec. Soc. Phys. Verein, Francof. ad Moenum. Soc. Honor. 
Principal and Professor of Physics in the City and Guilds of London 
Technical College, Finsbury. Morland, Chislett-road, West Hampstead. 
N.W. 

* Thomson, Joseph John, M.A. Sc.D. (Dubl.) Fellow of Trinity College and Caven- 
dish Professor of Experimental Physics, Cambridge. Trinity College, Cam- 
bridge. 

* Thome, Richard Thome, C.B. M.B. (Lond.) F.R.C.P. Medical Officer to 
H.M. Local Government Board, Vice-President of the Epidemiological 
Society, Lecturer on Public Health at the Medical Schoo of St. Bartholo- 
mew's Hospital. 45 Inverness-terrace. W. 

Thornycroft, John Isaac, M. Inst. C.E. Eyot Villa, Chisioick Mall, ChisivicL 
Thorpe, Thomas Edward, B.Sc. (Vict.) Sc.D. (Dubl.) Ph.D. (Heid.) LL.D. 

(Glasg.) Treas. C.S. Principal of the Government Laboratories, Somerset 

House, Fellow of the University of London, Soc. Chym. Berol. Socius. 

Soc. Phil. Glasc. Mem. Corr. Soc. Phil. Leeds, Lit. Phil. Mane. Soc. Honor. 

Government Laboratories, Somerset House, W.C. ; and Athenceum Club. 

s.w. 

■ Thuilher, Sir Henry Edward Landor, General, R.A. C.S.I. F.R.G.S. Tudor 
House, Richmond, Surrey ; and Oriental Club. W. 

f Tilden, William Augustus, D.Sc. (Lond. and Dubl.) F.C.S. F.I.C. Professor of 
Chemistry in the Royal College of Science, London. Hon. Mem. Pharm. 
Soc, Soc. Pub. Anal., Soc. Nat. Bristol, Coll. Pharm. Philad. 9 Ladbroke- 
gardens, Notting-hill. W. 
Tizard, Thomas Henry, Staff-Captain R.N., F.R.G.S. Hydrographic Depart- 
ment, Admiralty, Whitehall. S.W. 

* Todd, Sir Charles, M.A. (Camb.) K.C.M.G. F.R.A.S. Postmaster-General 

Superintendent of Telegraphs and Government Astronomer, South 
Australia. Tlie Observatory, Adelaide, South Australia. 
Tomes, Charles Sissmore, M.A. (Oson.). 9 Park-crescent, Portland-place. W. 
f Tomlinson, Charles, F.C.S. 7 North-road, Highgate. N. 

* Tomlinson, Herbert, B.A. (Oxon.). 88 Oakley-street, Chelsea. S.W. 

* Trail, James William Helenus, A.M. M.D. CM. (Aberd.) F.L.S. Regius Professor of 
Botany in the University of Aberdeen. The University, Aberdeen. N.B. 

* Traquair, Ramsay H., M.D. LL.D. F.R.S.E. F.G.S. Keeper of the Natural History 
Collections in the Museum of Science and Art, Edinburgh. 8 Dean Park- 
crescent, Edinburgh. 

f Trimen. Henry, M.B. F.L.S. Director of the Royal o t anic Gardens, Ceylon. 

Peradeniya, Ceylon; and Union Club. S.W. 
• Trimen, Roland, F.L.S. F.Z.S. F.E.S. Late Curator of the South African Museum. 

9, Osborne Mansions, Northumberland-street, Marylebone-road, W. ; and 

Oriental Club. W. 
Tristram, Rev. Henry Baker, M.A. (Oxon.) LL.D. (Edin.) D.D. C.M.Z.S. Canon of 

Durham. College, Durham. 



32 



Date of Election. 



June 7. 1877 



June 8, 1871 



June 4, 1886. 



June 7, 1894. 

June 7, 1883. 

June 2, 1870. 

June 4,1885. 



June 1, 18(35. 
June 7, 1883. 
June 1, 1893. 
June 2, 1892. 
Nov. 22, 1860. 
June 9, 1887. 

June 7, 1888. 

June 4, 1886. 

June 12, 1884. 
June 2,1881.' 



Sewed on 
Council. 

'90^91 



'93-94 



'90-92 



'85-86 
'90-92 



R. 
Dw. 



FELLOWS OF THE SOCIETY. (Nov. 30, 1895.) 

Turner, Sir William, M.B. (Lond.) D.C.L. (Dunelrn. et Oxon.) LL.D. (Glasg.) 
Sc.D. (Dubl.) F.R.C.S. (Edin.) F.R.C.S. F.R.S.E. Professor of Anatomy in 
the University of Edinburgh, Hon. Prof. Anat. Roy. Scot. Acad., Hon. 
Member Roy. Irish Acad., Hon. Fellow Roy. Med. Chir. Soc. London, Fos. 
Assoc. Anthrop. Soc. Paris, Cor. Member Soc. Anthrop. Etlmol. and 
Prehist. Arch. Berlin. 6 Eton-terrace, Edinburgh; and Athenatum Club. 
S.W. 

Tylor, Edward Burnett, D.C.L. (Oxon.) LL.D. (St. And. Aberd. and McGill) 
Assoc. Acad. Reg. Belg. Professor of Anthropology in the University of 
Oxford. Museum House, Oxford. 

Unwin, W. Cawthorne, B.Sc. Mem. Inst. C.E. Mem. Inst. M.E. Mem. 
Amer. Phil. Soc. Professor of Engineering at the Central Technical 
College of the City and Guilds of London Institute. 7 Palace Gate- 
mansions, Kensington. W. 

Veley, Victor Herbert, M.A. F.C.S. University College; and 22, Norham-road, 
Oxford. 

Venn, John, Sc.D. 3 St. Peter s-terrace, Cambridge. 

Verdon, The Hon. Sir George Frederic, C.B. K.C.M.G. The Melbourne Club, 
Melbourne, Australia; and Athenwum Club. S.W. 

Vines, Sydney Howard, M.A. (Oxon.) D.Sc. (Carnb. and Lond.) F.L.S. Sberardian 
Professor of Botany in the University of Oxford, Fellow of the University 
of London, Hon. Mem. Mane. Lit. Phil. Soc. and Roy. Phys. Soc. Edin., 
Corr. Mem. Soc. Nat. Sci. et Math, de Cherb. and Soc. Nat. Hist. Bost. 
Headington Hill, Oxford. 

Walker, James Thomas, General, C.B. R.E. LL.D. F.R.G.S. 13 Cromwell-road, 
South Kensington. S.W. 

Walker, John James, M.A. Mem. Lond. Math. Soc. and Mem. Phys. Soc. 12 
Denning-road, Hampstead. N.W. 

Wallace, Alfred Russel, LL.D. D.C.L. F.L.S. F.Z.S. Corfe View, Parkstone, 
Dorset. 

Waller, Augustus Desire, M.D. Lecturer on Physiology at St. Mary's Hospital 
Medical School. 16 Grove End-road. N.W. 

Walpole, Right Hon. Spencer Horatio, M.A. D.C.L. LL.D. Q.C. Trust. Brit. 
Mus. 109 Eaton-square, S.W. ; and Ealing. 

Walsingham, Thomas de Grey, Lord, M.A. LL.D., High Steward of the Univer- 
sity of Cambridge, Trust. Brit. Mus., F.L.S. F.Z.S. F.E.S., Mem. Soc. 
Ent. de France, Ent. Ver. zu Berlin, Nederlands Ent. Ver., Soc. Ent. de 
Russie, Linn. Soc. N.S.W. Merton Hall, Thetford, Norfolk. 

Ward, Harry Marshall, D.Sc. F.L.S. Late Fellow of Christ's College, Cambridge, 
Professor of Botany in the University of Cambridge. Botanical Laboratory, 
New Museums, Cambridge. 

Warington, Robert, M.A. (Oxon.) F.C.S. Sibthorpian Professor of Rural 
Economy in the University of Oxford. High Bank, Harpendcn, 
St. Albans. 

AVarren, Sir Charles, Major-General, R.E. K.C.B. G.C.M.G. Government 
House, Chatham ; and A thenamm Club. S.W. 

Watson, Rev. Henry William, D.Sc. The Rectory, Berkeswell, Coventry. 



Date of Election. 

June 5, 1890. 



Served on 
Council. 



FELLOWS OF THE SOCIETY. (Nov. 30, 1895.) 



33 



June 4. 1886. '8S-S9 



June 9, 1887. 



June 7, 1888. 



June 4, 1886 

June 2, 1870, 

June 5, 1862. 

June 7, 1855. 



'94-95 



June 12, i879. 

Jane 4, 1874. 

June 7, 1855. 
June 12, 1873, 



June 1, 1893 

June 6, 1889. 

June 1, 1893. 

June 3, 1852 



'59-61 
'69-71 
'73-90 



'89-90 



R. 



f Welclon, Walter Frank Raphael, M.A. Fellow of St. John's College, Jodrell 
Professor of Comparative Anatomy and Zoology at University College, 
London. 30a Wimpole-street. W. 

Wharton, William James Lloyd, Rear-Admiral, C.B. F.R.A.S. F.R.G.S. Hydro- 
grapher of the Admiralty. Florys, Princes-road, Wimbledon Park; and 
Ailienceum Club. S.W. 

Whitaker, William, B.A. F.G.S. Assoc. Inst. C.E. Geological Survey of 
England and Wales. Corr. Acad. Nat. Sci. Philad. 33 East Park-terrace, 
Southampton; and Geological Survey Office, 28 Jermyn-street. S.W. 

White, Sir William Henry, K.C.B. LL.D. (Glasg.) F.R.S.E. Mem. Inst. C.E. 
Fellow Royal School of Naval Architecture, V.P. Inst. Naval Architects, 
Assistant Controller and Director of Naval Construction. The Admiralty, 
Whitehall, S.W. ; and Athenamm Club. S.W. 

Wilde, Henry, Pres. Lit. Phil. Soc. Manch. The Hurst, Alderley Edge, Cheshire. 

■ Willis, Samuel, M.D. LL.D. Coll. Reg. Med. Soc. Consulting Physician to Guy's 
Hospital. 72 Grosvenor-street. W. 

Williams, C. Greville,F.C.S. F.I.C. Castlemaine, Oakhill-road, Putney. S.W. 
Williamson, Alexander William, Ph.D. (Giessen) D.C.L. (Dunelm.) LL.D. 

(Dubl. et Edin.) F.R.S.E. V.P.C.S. Hon. Mem. R.I.A. Fellow of Univ. 

Lond. Emeritus Prof, of Chemistry in Univ. Coll. Lond. Soc. Inst. Fr. 

(Acad. Sci.) Par. Acad. Reg. Sci. Berol. Acad. Reg. Sci. Taurin. Soc. 

Biol. Paris, Corr. Mem. Acad. Lync. Romas. Soc. Chem. Berol. et Amer. 

Nov. Ebor. Soc. Lit. Phil. Mane. Soc. Honor. Soc. Reg. Sci. Gott. Soc. 

Extr. High Pitfold, Shottermill, Haslemere. 
Williamson, Benjamin, M.A. D.Sc. D.C.L. (Oxon.) M.R.I.A. Fellow and Senior 

Tutor of Trinity College, Dublin. Trinity College, Dublin. 
\ Wilson, Sir Charles William, Major-General R.E. K.C.B. K.C.M.G. D.C.L. (Oxon.) 

LL.D. (Edin.) M.E. (Dubl.) F.R.G.S. Athenaeum Club. S.W. 
Wilson, George Fergusson, F.C.S. F.L.S. Heatherbank, Weybridge Heath, Surrey. 
\ Woodward, Henry, LL.D. (St. And.) P.G.S. F.Z.S. F.R.M.S. Lye. Hist. Nat. Nov. 

Ebor. et Soc. Phil. Amer. Philad. Soc. Soc. Phil. Ebor. Assoc. Geol. Lond. 

Socc. Geol. Edin.. Glasc. Liverp. et Nordov. Soc. Honor. Socc. Geol. Belg. 

Imp. Nat. Hist. Mosq. Hist. Nat. Montreal et Malacol. Belg. Corresp., Keeper 

of the Department of Geology, British Museum (Natural History), Cromwell- 
road, S.W. 129 Beaufort-street, Chelsea. S.W. 

• Worthington, Arthur Mason, M.A. F.R.A.S. Headmaster and Professor of 
Physics, Royal Naval Engineeiing College, Devonport. 6 Osborne Villas, 
Devonport. 

■ Yeo, Gerald Francis, M.D. (Dublin) F.R.C.S. Emeritus Professor of Physiology 
in King's College, London. Boivden, Totnes, South Devon. 

• Young, Sydney, D.Sc. (Lond.) F.C.S. F.I.C. Professor of Chemistry in 
University College, Bristol. 13 Aberdeen - road, White Ladies' - road, 
Bristol. 

• Younghusband, Charles Wright, Lieut-General, O.B. Palace-court-mansions, 
Bayswater-road, W. ; and A thenwum Club. S.W. 



E 



FOREIGN MEMBERS. 



fQto- 



D. 
D. 



CD. 
C. 



fim. 



Km. 



Rm 



Em. 
C. 



Agassiz, Alexander Camb. (Mass). 1891. 

Auwers, Georg Friedricli 

Julius Arthur , . Berlin. 1 879. 

Baeyer, Adolf von Munich. 1885. 

Berthelot, Marcelliu Paris. 1877. 

Bertrand, Joseph Louis 

Francois , . Paris. 1875. 

Bunsen, Robert Wilhelm .... Heidelberg. 1858. 

Cannizzaro, Stanislao Rome. 1889. 

Chauveau, Jean Baptiste 

Auguste Paris. 1889. 

Cornu, Alfred Paris. 1884. 

Cremona, Luigi Rome. 1879. 

Daub re e, Gabriel Auguste . . Paris. 1881. 

Des Cloizeaux, Alfred Louis 

Olivier Paris. 1875. 

Du Bois-Reymond, Emil Hein- 

rich Berlin. 1877. 

Fizeau, Hippolyte Louis .... Paris. 1875. 

Gegenbaur, Carl Heidelberg. 1884. 

Gould, Benjamin Apthorp Camb.(Mass.). 1891. 

Hermite, Charles Paris. 1873. 

Janssen, Pierre Jules Cesar . . Paris. 1875. 

Kekule, August Bonn. 1875. 

Klein, Felix Gottingen. 1885. 



D. 



Rm. 
C. 
C. 



Kolliker. Albert von Wiirzburg. 1860. 

Kowalewski, Alexsandr. . . . St. Petersburg. 1885. 

Ktihne, Willy Heidelberg. 1892. 

Leuckart, Rudolph. Leipsic. 1877. 

Mascart, Eleuthere Elie Nicolas Paris. 1892. 

Mendeleeff, Dmitri Ivanovitch 

St. Petersburg. 18^2. 

Newcomb, Simon Washingtonl811 . 

Newton, Hubert Anson New Haven.18^2. 

Pfliiger, Eduard Friedrich 

Wilhelm , Bonn. 1888. 

Poincare, Henri Paris. 1894. 

Quincke, Georg Hermann. „ . . Heidelberg. 1879. 
Rowland, Henry A. ........ Baltimore. 1889. 

Sachs, Julius von Wiirzburg. 1888. 

Steenstrup, Johannes Japetus 

Smith Copenhageu.lSbo. 

Strasburger, Eduard. ....... Bonn. 1891. 

Struve, Otto Wilhelm . . . . Pulkowa. 1873. 

Suess, Eduard Vienna. 189-1. 

Tacchini, Pietro Rome. 1891. 

Virchow, Rudolf Berlin. 1884. 

Weierstrass, Carl ....,.,„,. Berlin. 1881. 
Wiedemann, Gustav . . ..«>., Leipsic. 1884. 



FELLOWS DECEASED SINCE THE LAST ANNIVERSARY (Nov. 30, 1894). 



On 

Aberdare, Henry Austin Bruce, Lord, G.C.B. 

Babington, Charles Cardale, M.A. 

Ball Valentine, C.B. 

Beetbam, Albert William. 

Bristowe, John Syer, M.D. 

Buchanan, Sir George, M.D. 

Carter, Henry John, Surge.on-Major. 

Cayley, Arthur, D.C.L- 

Cockle, Sir James, M.A. 

Dobson, George Edward, M.A. 



the Home List. 

Hawkins, Bisset, M.D. 

Hulke, John Whitaker, P.R.C.S. 

Huxley, Right Hon. Thomas Henry, D.C.L. 

Kirkman, Rev. Thomas Penyngton, M.A. 

Rawlinson, Sir Henry Creswicke, Bart., G.CB. 

Savory, Sir William Scovell, Bart. 

Selborne, Roundell Palmer, Earl of. 

Tomes, Sir John E.R.C.S. 

Williamson, William Crawford, LL.D 



On the Foreign List. 



Baillon, Henri Ernest. 
Dana, James Dwight. 
Loven, Sven Ludwig. 
Ludwig, Carl. 



Neumann, Franz Ernst. 
Pasteur, Louis. 
Tchebitchef, Pafnutij. 



Change of Name and Title. 
Worms, Baron Henry de, to Lord Pirbright. 



FELLOWS ELECTED SINCE THE LAST ANNIVERSARY. 



1895. June 13. *Barry, J. Wolfe, C.B. 
169.5. June 13. *Boume, Prof. Alfred Gibbs, D.Sc. 
1895. Jane 13. *Biyan, George Hartley, M.A. 
1895. Jan. 24. j fDavey, Right Hon. Horace, Lord, 

D.C.L. 
1895. June 13. *Eliot, John, M.A. 
1895. June 13. *Green, Prof. Joseph Reynolds, 

D.Sc. 
1895. June 13. *Griffiths, Ernest HoAvard, M.A. 
1895. June 13. Heycock, Charles Thomas, M.A. 



1895. June 13. 
1895. June 13. 



1895. 
1895. 
1895. 
1895. 
1895. 
1895. 



June 13. 
June 13. 
June 13. 
June 13 
June 13. 
June 13. 



*Hickson, Prof. Sydney John, 

D.Sc. 
*Holden, Major Henry Capel Lofft. 

R.A. 
*McClean, Frank, M.A., LL.D. 
*Macewen, Prof. William, M.D. 
*Martin, Sidney, M.D. 
*Minchin, Prof. George M., M.A. 
*Power, William Henry 
*Purdie, Prof. Thomas, B.Sc. 



NAMES OF PERSONS TO WHOM THE MEDALS 



OF 



THE EOYAL SOCIETY HAVE BEEN AWARDED. 



COPLEY MEDAL. 



1731. 
1732. 
1734. 
1736. 
1737. 
1738. 
1739. 
1740. 
1741. 
1742. 

1743. 
1744. 
1745. 
1746. 
1747. 
1748. 
1749. 
1750. 
1751. 
1752. 
1753. 
1754. 
1755. 
1757. 
1758. 
1759. 
1760. 
1764. 
1766. 



1767 

1768 



Stephen Gray. 
Stephen Gray. 
John Theophilus Desaguliers. 
John Theophilus Desaguliers. 
John Belchier. 
James Valoue. 
Stephen Hales. 
Alexander Stuart. 
John Theophilns Desaguliers 
Captain Christopher Middle- 
ton. 
Abraham Trembley. 
Henry Baker. 
Sir William "Watson. 
Benjamin Robins. 
Gowin Knight. 
Rev. James Bradley. 
John Harrison. 
George Edwards. 
John Canton. 
Sir John Pringle. 
Benjamin Franklin. 
William Lewis. 
John Huxhani. 
Lord Charles Cavendish. 
John Dollond. 
John Smeaton. 
Benjamin Wilson. 
John Canton. 
William Brownrisrsj. 

CO 

Edward Delaval. 
Hon. Henry Cavendish. 
John Ellis. 
Peter Woulfe. 



1769. 


William Hewson. 


1806. 


1770. 


Sir William Hamilton. 


1807. 


1771. 


Matthew Raper. 


1808. 


1772. 


Joseph Priestley. 


1809. 


1773. 


John Walsh. 


1811. 


1775. 


Rev. Nevil Maskelyne. 


1813. 


1776. 


Captain James Cook. 


1814. 


1777. 


John Mudge. 


1815. 


1778. 


Charles Hutton. 


1817. 


1780. 


Rev. Samuel Vince. 


1818. 


1781. 


Sir William Herschel. 


1820. 


1782. 


Richard Kirwan. 


1821. 


1783. 


John Goodricke. 
Thomas Hutehins. 




1784. 


Edward Waring. 


1822. 


1785. 


Major-General William Roy. 


1823. 


1787. 


John Hunter. 


1824. 


1788. 


Sir Charles Blagden. 




1789. 


William Morgan. 


1825. 


1791. 


James Rennell. 






John Andrew De Luc. 


1826. 


1792. 


Benjamin Count Rumford. 


1827. 


1794. 


Professor Yolta. 




1795. 


Jesse Ramsden. 


1831. 


1796. 


George Attwood . 


1832. 


1798. 


Sir George Shuckburgh 






E velyn. 


1834. 




Charles Hatchett. 


1835. 


1799. 


Rev. John Hellins. 


1836. 


1800. 


Edward Howard. 




1801. 


Sir Ashley Paston Cooper. 


1837. 


1S02. 


William Hyde Wollaston. 


1837. 


1S03. 


Richard Chenevix. 


1838. 


1S04. 


Smithson Tennant. 


1S38. 


1805. 


Sir Humphry Davy. 


1839. 



Thomas Andrew Knight. 
Sir Everai'd Home. 
William Henry. 
Edward Troughton. 
Benjamin Collins Brodie. 
William Thomas Brando. 
James Ivory. 
David Brewster. 
Captain Henry Kater. 
Sir Robert Seppings. 
John Christian Oersted. 
Captain Edward Sabine. 
John Frederick William 

Herschel. 
Rev. William Buckland. 
John Pond. 
John Brinkley, Bishop of 

Cloyne. 
Francois Arago. 
Peter Barlow. 
Sir William South. 
William Prout. 
Captain Henry Foster. 
George Biddell Airy. 
Michael Faraday. 
Baron Simeon Denis Poisson. 
Giovanni Plana. 
William Snow Harris. 
Jons Jacob Berzelins. 
Francis Kiernan. 
Antoine C. Becqnerel. 
John Frederic Daniel], 
Karl Friedrich Gauss. 
Michael Faraday. 
Robert Brown. 



COPLEY MEDAL— continued. 



1840. 


Justus Liebig. 


1856 




Jacques Charles Francois 


1857 




Sturm. 


1858 


1841. 


George Simon Okm. 


1859 


1842. 


James MacCullagh. 


1860. 


1843. 


Jean Baptiste Dumas. 


1861 


1844. 


Carlo Matteucci. 


1862 


1845. 


Theodor Schwann. 


1863. 


1846. 


TTrbainJeanJosephLeVerrier. 


1864 


1847. 


Sir John. Frederick William 


1865 




Herschel. 


1866 


1848. 


John Couch Adams. 


1867 


1849. 


Sir Roderick Impey Mur- 


1868 




chison. 


1869. 


1850. 


Peter Andreas Hansen. 


1870 


1851. 


Richard Owen. 


1871 


1852. 


Baron Alexander von Hum- 


1872. 




boldt. 


1873 


1853. 


Heinrich Wilhelm. Dove. 




1854. 


Johannes Miiller. 


1874 


1855. 


Jean Bernard Leon Foucanlt. 


1875. 



Henry Milne-Edwards. 
Michel Eugene Chevreul. 
Sir Charles Lyell. 
Wilhelm Eduard Weber. 
Robert Wilhelm Bnnsen 
Louis Agassiz. 
Thomas Graham. 
Rev. Adam Sedgwick. 
Charles Darwin. 
Michel Chasles. 
Julius Pliieker. 
Karl Ernst von Baer. 
Sir Charles Wheatstone. 
Henri Victor Regnault. 
James Prescott Joule. 
Julius Robert Mayer. 
Friedrich Wokler. 
Hermann Ludwig Ferdinand 

Helmholtz. 
Louis Pasteur. 
Auo-ust Wilhelm Hofmann. 



1876. Claude Bernard. 

1877. James Dwight Dana. 

1878. Jean Baptiste Bonssingault. 

1879. Rudolph J. E. Clansius. 

1880. James Joseph Sylvester. 

1881. Karl Adolph Wiirtz. 

1882. Arthur Cayley. 

1883. Sir William Thomson. 

1884. Carl Ludwig. 

1885. August Kekule. 

1886. Franz Ernst Neumann. 

1887. Sir Joseph Dalton Hooker. 

1888. Thomas Henry Huxley. 

1889. Rev. George Salmon. 

1890. Simon Newcomb. 

1891. Stanislao Cannizzaro. 

1892. Rudolf Virchow. 

1893. Sir George Gabriel Stokes. 

1 894. Edward Frankland. 

1895. Carl Weierstrass 



RUMFORD MEDAL. 



1S00. 


Benjamin Count Ramford. 


1848. 


1804. 


John Leslie. 


1850. 


1806. 


William Murdoch. 




1810 


Etienne Louis Malus. 


1852 


1814. 


William Charles Wells. 


1854 


1816. 


Sir Humphry Davy. 


1856 


1818. 


David Brewster. 


1858 


1824. 


Augustin Jean Fresnel. 


1860 


1832. 


John Frederic Daniell. 


1862 


1834. 


Macedonio Melloni. 


1864 


1838. 


James David Forbes. 


1866 


1810. 


Jean Baptiste Biot. 




1-4:2. 


Henry Fox Talbot. 


1868 


1846. 


Michael Faraday. 


1870 



Henri Victor Regnault. 
Francois Jean Dominique 

Arago. 
George Gabriel Stokes. 
Neil Amott. 
Louis Pasteur. 
Jules Jamiu. 
James Clerk Maxwell. 
Gustav Robert Kirchhoff. 
John Tyndall. 
Armand Hippolyte Louis 

Fiaeau. 
Balfour Stewart. 
Alfred Olivier Des Cloizeaux. 



o 

1872. Anders Jonas Angstrom. 
1874. Joseph Norman Lockyer. 
1876. Pierre Jules Cesar Janssen. 
1878. Alfred Cornu. 
1880. William Huggins. 
1882. William de W. Abney. 
1884. Tobias Robertus Tbalen. 
1886. Samuel Pierpont Langley. 
1888. Pietro Tacchini. 
1 890. Heinrich Hertz. 
1892. Nik C. Duner. 
1894. James Dewar. 



EOYAL MEDAL. 



1826. John Dalton. 
James Ivory. 

1827. Sir Humphry Davy. 
Friedrich Georg Wilhelm 

Strove. 

1828. Johann Friedrich Encke. 
William Hyde Wollaston. 

1829. Charles Bell. 
Eilhard Mitscherlich . 

1830. David Brewster. 
Antoine Jerome Balard. 

1833. Auguste Pyrame De Can- 

dolle. 
Sir John Frederick William 
Herschel. 

1834. John William Lubbock. 
Charles Lyell. 

1835. Michael Faraday. 

Sir William Rowan Hamilton. 

1836. George Newport. 

Sir John F. W. Herschel. 

1837. Rev. William Whewell. 

1838. Thomas Graham. 
Henry Fox Talbot. 

1839. James Ivory. 

Dr. Martin Barry. 

1840. Sir John F. W. Herschel. 
Charles Wheatstone. 

1841. Robert Kane. 
Eaton Hodgkinson. 

•1842. William Bowman. 

John Frederic Daniell. 

1843. James David Forbes. 
Charles Wheatstone. 

1844. Thomas Andrews. 
George Boole. 

1845. George Biddell Airy. 
Thomas Snow Beck. 

1846. Michael Faraday. 
Richard Owen. 

L847. George Fownss. 

William Robert Grove. 

1848. Thomas Galloway. 
Charles James Hargreave. 

1849. Colonel Edward Sabine. 
Gideon A. Mantel]. 

1850. Benjamin Collins Brodie. 
Thomas Graham. 



1851. Earl of Rosse. 
George Newport. 

1852. James Prescott Joule. 
Thomas Henry Huxley. 

1853. Charles Darwin. 

1854. August Wilhelm Hofmann. 
Joseph Dalton Hooker. 

1855. John Russell Hind. 
John Obadiah Westwood. 

1856. Sir John Richardson. 
William Thomson. 

1857. Edward Frankland. 
John Lindley. 

1858. Albany Hancock. 
William Lassell. 

1859. George Bentham. 
Arthur Cayley. 

1860. WilHam Fairbairn. 
Augustus Waller. 

1861. WilHam B. Carpenter. 
James Joseph Sylvester. 

1862. Rev. Thomas Romney Robin- 

son. 
Alexander William William- 
son. 

1863. Rev. Miles J. Berkeley. 
John Peter Gassiot. 

1864. Jacob Lockhart Clarke. 
Warren De La Rue. 

1865. Joseph Prestwich. 
Archibald Smith. 

1866. William Huggins. 
William Kitchen Parker. 

1867. John Bennet Lawes and 

Joseph Henry Gilbert. • 
Sir William Logan. 

1868. Alfred Russel Wallace. 
Rev. George Salmon. 

1869. Sir Thomas Maclear. 
Augustus Matthiessen. 

1870. William Hallowes Miller. 
Thomas Davidson, 

1871. John Stenhouse. 
George Busk. 

1872. Thomas Anderson. 
Henry John Carter. 

1873. George James Allman. 
Henry Enfield Roscoe. 



1874. Henry Clifton Sorby. 
WilliamCrawf ordWilliamsou . 

1875. WilHam Crookes. 
Thomas Oldham. 

1876. William Froude. 

Sir C. Wyviile Thomson. 

1877. Frederick Augustus Abel. 
Oswald Heer. 

1878. John Allan Broun. 
Albert C. L. G. Gunther. 

1879. William Henry Ferkin. 
Andrew Crombie Ramsay. 

1880. Joseph Lister. 
Andrew Noble. 

1881. Francis Maitland Balfour. 
John Hewitt Jellett. 

1882. William Henry Flower. 
Lord Rayleigh. 

1883. Thomas Archer Hirst. 
J. S. Burdon Sanderson. 

1884. George Howard Darwin. 
Daniel OHver. 

1885. David Edward Hughes. 
Edwin Ray Lankester. 

1886. Francis Galton. 
Peter Guthrie Tait. 

1887. Colonel Alexander R.oss 

Clarke. 
Henry Nottidge Moseley. 

1888. Baron Ferdinandvon Mueller. 
Osborne Reynolds. 

1889. Walter Holbrook Gaskeli. 
Thomas Edward Thorpe. 

1890. David Ferrier. 
John Hopkinson. 

1891. Charles Lapworth. 
Arthur William Rucker. 

1892. John Newport Langley. 
Rev. Charles Pritchard. 

1893. Arthur Schuster. 
Harry Marshall Ward. 

1894. Victor Alexander Haden 

Horsley. 
Joseph John Thomson. 

1895. James Alfred Ewing. 
John Murray. 



DAVY MEDAL. 



1877. 


.Robert Wiihelm Bunsen. 


1885. 




Gustav Kobert Kirchhoff. 


1886. 


1878. 


Louis Paul Cailletet. 


1887. 




Raoul Pictet. 


1888. 


1879. 


Paul Emile Lecoq de Boisbaudran. 


1889. 


1880. 


Charles Priedel. 


1890. 


1881. 


Adolf Baeyer. 


1891. 


1882. 


Dimitri Ivanovitch Mendeleeff. 


1892, 




Lotliar Meyer. 


1893. 


1S83. 


Marcellin Bertlielot. 






Julius Thoinsen. 


1894. 


1884. 


Adolph Wilhelm Hermann Kolbe. 


1895. 



Jean Servais Stas. 

Jean Charles (lalissard de Marignac. 

John A. R. Newlands. 

William. Crookes. 

William Hemy Perkin. 

Bmil Piseher. 

Victor Meyer. 

Francois Marie Raoult. 

J. H. van't Hoff. 

J. A. Le Bel. 

Per Theodor Cleve. 

William Ramsay. 



DARWIN MEDAL. 

1890. Alfred Russel Wallace. 
1892. Sir Joseph Dalton Hooker. 
1894. Thomas Henry Huxley. 



BAhRISON AND SONS, PRINTERS IS ORDINARY TO HER MAJESTT, ST. MARTINS LANE, LONDON, 



PHILOSOPHICAL 



TRANSACTIONS 



OF THE 



ROYAL SOCIETY 



OF 



LONDON. 



(A.) 



FOR THE YEAR MDCCCXCV. 



VOL. 186.— PART I. 



LONDON: 

PRINTED BY HARRISON AND SONS, ST. MARTIN'S LANE, W.C. 
|)rinto in ©rbinarg to *§a Ulajtsig. 

MDCCCXCV. 



ADVERTISEMENT. 



The Committee appointed by the Royal Society to direct the publication of the 
Philosophical Transactions take this opportunity to acquaint the public that it fully 
appears, as well from the Council-books and Journals of the Society as from repeated 
declarations which have been made in several former Transactions, that the printing of 
them was always, from time to time, the single act of the respective Secretaries till 
the Forty-seventh Volume ; the Society, as a Body, never interesting themselves any 
further in their publication than by occasionally recommending the revival of them to 
some of their Secretaries, when, from the particular circumstances of their affairs, the 
Transactions had happened for any length of time to be intermitted. And this seems 
principally to have been done with a view to satisfy the public that their usual 
meetings were then continued, for the improvement of knowledge and benefit of 
mankind : the great ends of their first institution by the Royal Charters, and which 
they have ever since steadily pursued. 

But the Society being of late years greatly enlarged, and their communications more 
numerous, it was thought advisable that a Committee of their members should be 
appointed to reconsider the papers read before them, and select out of them such as 
they shoidd judge most proper for publication in the future Transactions ; which was 
accordingly done upon the 26th of March, 1752. And the grounds of their choice are, 
and will continue to be, the importance and singularity of the subjects, or the 
advantageous manner of treating them ; without pretending to answer for the 
certainty of the facts, or propriety of the reasonings contained in the several papers 
so published, which must still rest on the credit or judgment of their respective 
authors. 

It is likewise necessaiy on this occasion to remark, that it is an established rule of 
the Society, to which they will always adhere, never to give then opinion, as a Body, 



[ iv ] 

upon any subject, either of Nature or Art, that comes before them. And therefore the 
thanks, which are frequently proposed from the Chair, to be given to the authors of 
such papers as are read at their accustomed meetings, or to the persons through whose 
hands they received them, are to be considered in no other light than as a matter of 
civility, in return for the respect shown to the Society by those communications. The 
like also is to be said with regard to the several projects, inventions, and curiosities of 
various kinds, which are often exhibited to the Society ; the authors whereof, or those 
who exhibit them, frequently take the liberty to report, and even to certify in the 
public newspapers, that they have met with the highest applause and approbation. 
And therefore it is hoped that no regard will hereafter be paid to such reports and 
public notices ; which in some instances have been too lightly credited, to the 
dishonour of the Society. 



1895. 



List of Institutions entitled to receive the Philosophical Transactions or 

Proceedings of the Royal Society. 



Institutions marked a are entitled to receive Philosophical Transactions, Series A, and Proceedings. 
„ „ b „ „ „ „ Series B, and Proceedings. 

„ ,, ae „ „ „ Series A and B, and Proceedings. 

V » Proceedings only. 



America (Central). 
Mexico. 

p. Sociedad Cientifica " Antonio Alzate." 
Ameriea(North). (See United States and Canada.) 
America (South). 
Buenos Ayres. 

ab. Museo Nacional. 
Caracas. 

B. University Library. 
Cordova. 

ab. Acadeniia Nacional de Ciencias. 
Demerara. 
p. Royal Agricultural and Commercial 
Society, British Guiana. 
La Plata. 

b. Museo de La Plata. 
Rio de Janeiro. 
p. Observatorio. 
Australia. 
Adelaide. 
p. Royal Society of South Australia. 

Brisbane. 

p. Royal Society of Queensland. 
Melbourne. 

p. Observatory. 

p. Royal Society of Victoria. 

ab. University Library. 
Sydney. 



Australian Museum. 

Geological Survey. 

Linnean Society of New South Wales. 

Royal Society of New South Wales. 

University Library. 



P- 

P- 
V- 

ab. 
ab. 
Austria. 
Agram. 
p. Jugoslavenska Akademija Znanosti i Um- 

jetnosti. 
p. Societas Historico-Naturalis Croatica. 

MDCCCXCV. — A. 



Austria (continued). 
Briinn. 

ab. Naturforschender Verein. 
Gratz. 

AB. Naturwisseuschaftlicher Verein fur Steier- 
mark. 
Innsbruck. 

ab. Das Ferdinandeum. 

p. Naturwissenschaftlich • Medicinischer 
Verein. 
Prague. 

ab. Konigliche Bohmische Gesellschaft der 
Wissenschaften. 
Trieste. 

b. Museo di Stovia Naturale. 
p. Societa Adriatica di Scienze Naturali. 
Vienna. 
p. Antbropologische Gesellschaft. 

Kaiserliche Akademie der Wissenschaften, 
K.K. Geographische Gesellschaft. 
K.E. Geologische Reichsanstalt. 
K.K. Naturhistorisches Hof- Museum. 
K.K. Zoologisch-Botanische Gesellschaft. 
Oesterreichische Gesellschaft fiir Meteoro- 

logie. 
Von Kuffner'sche Stemwarte. 
Belgium. 
Brussels. 

b. Academie Royale de Meclecine. 
Acadende Royale des Sciences. 
Musee Royal d'Histoire Naturelle dc 

Belgique. 
Observatoire Royal. 
Societe Beige de Geologie, de Paleonto- 

logie, et d'Hydrologie. 
Societe Malacologique de Belgique. 



ab. 

P- 
ab. 

B 
B. 

P- 
A. 



AB. 
b. 

P- 
P- 



Ghent. 

AB. University. 



VI 



Belgium (continued). 
Liege, 

AB. Societe des Sciences. 

p. Societe Geologique de Belgique. 
Louvain. 

B. Laboratoire de Microscopie et de Biologie 
Cellulaire 

AB. Universite. 
Canada. 
Hamilton. 

p. Hamilton Association. 
Montreal. 

ab. McGill University. 

p. Natural History Society. 
Ottawa. 

ab. Geological Survey of Canada. 

ab. Royal Society of Canada. 
Toronto. 

p. Astronomical and Physical Society. 

p. Canadian Institute. 

ab. University. 
Cape of Good Hope. 

a. Observatory. 

ab. South African Library. 
Ceylon. 
Colombo. 

B. Museum. 
China. 
Shanghai. 

p. China Branch of the Royal Asiatic Society. 
Denmark. 
Copenhagen. 

ab. Kongelige Danske Videnskabernes Selskab. 
Egypt. 

Alexandria. 

ab. Bibliotheque Municipale. 
England and Wales. 
Aberystwith. 

ab. University College. 
Bangor. 

ab. University College of North Wales. 
Birmingham. 

ab. Free Central Library. 

ab. Mason College. 

p. Philosophical Society. 
Bolton. 

p. Public Library. 
Bristol. 

p. Merchant Venturers' School. 

ab. University College. 
Cambridge. 

ab. Philosophical Society. 

p. Union Society. 



England and Wales (continued). 
Cooper's Hill. 

ab. Royal Indian Engineering College. 
Dudley. 

p. Dudley and Midland Geological 
Scientific Society. 
Essex. 

p. Essex Field Club. 
Falmouth. 

p. Royal Cornwall Polytechnic Society. 
Greenwich. 

A. Royal Observatory. 
Kew. 

b. Royal Gardens. 
Leeds. 

p. Philosophical Society. 

AB. Yorkshire College. 
Liverpool. 

ab. Free Public Library. 

p. Literary and Philosophical Society. 

a. Observatory. 

ab. University College. 
London. 

ab. Admiralty. 

p. Anthropological Institute. 

ab. British Museum (Nat. Hist.). 

ab. Chemical Society. 

A. City and Guilds of London Institute. 
p. " Electrician," Editor of the. 

B. Entomological Society. 
ab. Geological Society. 

ab. Geological Survey of Great Britain. 

p. Geologists' Association. 

ab. Guildhall Library. 

A. Institution of Civil Engineers. 

p. Institution of Electrical Engineers. 

a. Institution of Mechanical Engineex'S. 
a Institution of Naval Architects. 

p. Iron and Steel Institute. 
ab. King's College. 

b. Linnean Society. 
ab. Loudon Institution. 
p. London Library. 

a. Mathematical Society. 

p. Meteorological Office. 

p. Odontological Society. 

p. Pharmaceutical Society. 

p. Physical Society. 

p. Quekett Microscopical Club. 

p. Royal Agricultural Society. 

p. Royal Asiatic Society. 

a. Royal Astronomical Society. 

b. Royal College of Physicians. 
b. Royal College of Surgeons. 



and 



Vll 



England and Wales (continued). 
London (continued). 

p. Royal Engineers (for Libraries abroad, six 
copies) . 

ab. Royal Engineers. Head Quarters Library. 

p. Royal Geographical Society. 

p. Royal Horticultural Society. 

p. Royal Institute of British Architects. 

ab. Royal Institution of Great Britain. 

B. Royal Medical and Chirurgical Society. 

p. Royal Meteorological Society. 

p. Royal Microscopical Society. 

p. Royal Statistical Society. 

ab. Royal United Service Institution. 

ab. Society of Arts. 

p. Society of Biblical Archaeology. 

p. Society of Chemical Industry (London 
Section). 

p. Standard Weights and Measures Depart- 
ment. 

ab. The Queen's Library. 

ab. The War Office. 

ab. University College. 

p. Victoria Institute. 

B. Zoological Society. 
Manchester. 

ab. Free Library. 

ab. Literary and Philosophical Society. 

p. Geological Society. 

ab. Owens College. 
Netley. 

p. Royal Victoria Hospital. 
Newcastle. 

ab. Free Library. 

p. North of England Institute of Mining and 
Mechanical Engineers. 

p. Society of Chemical Industry (Newcastle 
Section) . 
Norwich. 

p. Norfolk and Norwich Literary Institution. 
Nottingham. 

ab. Free Public Libiary. 
Oxford. 

p. Ashmolean Society. 

ab. Radcliffe Library. 

a. Radcliffe Observatory. 
Penzance. 

p. Geological Society of Cornwall. 
Plymouth. 

b. Marine Biological Association. 
p. Plymouth Institution. 

Richmond. 

a. " Kew" Observatory. 



England and Wales (continued). 
Salford. 

p. Royal Museum and Library. 
Stonyhurst. 

p. The College. 
Swansea. 

ab. Royal Institution. 
Woolwich. 

ab. Royal Artillery Library. 
Finland. 
Helsingfors. 

p. Societas pro Fauna et Flora Fennica. 

ab. Societe des Sciences. 
France. 
Bordeaux. 

p. Academie des Sciences. 

p. Faculte des Sciences. 

p. Societe de Medecine et de Chirurgie. 

p. Societe des Sciences Physiques et 
Naturelles. 
Cherbourg. 

p. Societe des Sciences Naturelles. 
Dijon. 

p. Academie des Sciences. 
Lille. 

p. Faculte des Sciences. 
Lyons. 

ab. Academiedes Sciences, Belles-Lettres et Arts. 

ab. Universite. 
Marseilles. 

p. Faculte des Sciences. 
Montpellier. 

ab. Academie des Sciences et Lettres. 

b. Faculte de Medecine. 
Nantes. 

p. Societe des Sciences Naturelles de l'Ouest 
de la France. 
Paris. 

ar. Academie des Sciences de lTnstitut. 

p. Association Francaise pour l'Avancement 
des Sciences. 

p. Bureau des Longitudes. 

a. Bureau International des Poids et Mesures. 

p. Commission des Annales des Ponts et 
Chaussees. 

p. Conservatoire des Arts et Metiers. 

p. Cosmos (M. l'Abbe Valette). 

ab. Depot de la Marine. 

ab. iCcole des Mines. 

ab. Ecole Normale Superieure. 

ab. Ecole Polvtechnique. 

ab. Faculte des Sciences de la Sorbonne. 

ab. Jardin des Plantes. 

p. L'Electricien. 



b 2 



[ viii ] 



France (continued). 
Paris (continued). 
a. L'Observatoire. 

p. Revue Scientifique (Mons. H. r>E Varjgny). 
p. Societe de Biologie. 
ab. Societe d'Encouragement pour l'lndustrie 

Nationale. 
ab. Societe de Geographic 
p. Societe de Physique. 
B. Societe Eutomologique. 
ab. Societe Geologique. 
p. Societe Mathematique. 
p. Societe Meteorologique de France. 
Toulouse. 

ab. Academie des Sciences. 
a. Faculte des Sciences. 
Germany. 
Berlin. 

A. Deutsche Chemische Gesellsehaft. 

A. Die Sternwarte. 

p. Gesellsehaft fur Erdkunde. 

ab. Konigliche Preussische Akademie der 

Wissenschaften. 
a. Physikalisehe Gesellsehaft. 
Bonn. 

ab. Universitat. 
Bremen. 

p. Naturwissenschaftlicher Verein. 
Breslan. 

p. Schlesische Gesellsehaft fur Vaterlandische 
Kultur. 
Brunswick. 

p. Verein fur Naturwissenscha.fi. 
Carlsruhe. See Karlsruhe. 
Charlottenburg. 

A. Physikalisch-Technische Reiclisanstalt. 
Danzig. 

ab. Naturforschende Gesellsehaft. 
Dresden. 

p. Yerein fiir Erdkunde. 
Emden. 

p. Naturforschende Gesellsehaft. 
Erlangen. 

ab. Physikaliseh-Medicinisehe Societat. 
Frankfurt-ani-Main. 

ab. Senckenbergiscke Naturforschende Gesell- 
sehaft. 
p. Zoologische Gesellsehaft. 
Frankfurt-am-Oder. 

p. Naturwissenschaftlicher Verein. 
Freiburg-im-Breisgau. 

ab. Universitat. 
Giessen. 

ab. Grossherzogliche Universitat. 



Germany (continued). 
Gorlitz. 

p. Natnrforschende Gesellsehaft. 
Gottingen. 

ab. Konigliche Gesellsehaft der Wissenschaften. 
Halle. 

ab. Kaiserliche Leopoldino - Carolinische 

Deutsche Akademie der Naturforscher. 

p. Naturwissenschaftlicher Verein fiir Sach- 
sen und Thiiringen. 
Hamburg. 

p. N~aturhistorisch.es Museum. 

ab. Naturwissenschaftlicher Verein. 
Heidelberg. 

p. Naturhistoriseh-Medizinischer Verein 

ab. Universitat. 
Jena. 

ab. Medicinisch-Naturwissenschaftliche Gesell- 
sehaft. 
Karlsruhe. 

a. Grossherzogliche Sternwarte. 

p. Teehnische Hochschule. 
Kiel. 

p. Naturwissenschaftlicher Verein fiir 
Schleswig-Holstein. 

A. Sternwarte. 

ab. Universitat. 
Kiinigsberg. 

ab. Konigliche Physikalisch - Okonomische 
Gesellsehaft. 
Leipsie. 

p. Annalen der Physik und Chemie. 

A. Astronomische Gesellsehaft. 

ab. Konigliche Sachsische Gesellsehaft der 
Wissenschaften. 
Magdeburg. 

p. Naturwissenschaftlicher Verein. 
Marburg. 

ab. Universitat. 
Munich. 

ab. Konigliche Bayerische Akademie der 
Wissenschaften . 

p. Zeitschrift fiir Biologie. 
Milnster. 

ab. Konigliche Theologische und Philo- 
sophische Akademie. 
Potsdam. 

a. Astrophysikalisches Observatorium. 
Rostock. 

ab. Universitat. 
Strasburg. 

ab. Universitat. 
Tubingen. 

ab. Universitat. 



IX 



Germany (continued). 
Wiirzburg. 

ab. Physikalisch-Medicinisehe Gesellschaft. 
Greece. 
Athens. 

A. National Observatory. 
Holland. (See Netherlands.) 
Hungary. 
Bnda-pest. 

p. Konigl. TJngarische Geologische Anstalt. 
ab. A Magyar Tudos Tarsasag. Die Ungariscbe 
Akademie der Wissenschaften. 
Hermannstadt. 
p. Siebenbiirgiscber Verein fiir die Natur- 
"wissenschaf ten . 
Klausenbnrg. 

ab. Az Erdelyi Muzeum. Das Siebenbiirgische 
Museum. 
Scbemnitz. 
p. K. Ungarische Berg- und Forst- Akademie, 
India. 
Bombay. 

ab. Elphinstone College. 

p. Roval Asiatic Society (Bombay Branch). 
Calcutta. 

ab. Asiatic Society of Bengal. 
ab. Geological Museum. 

p. Great Trigonometrical Survey of India. 
ab. Indian Museum. 

p. The Meteorological Reporter to the 
Government of India. 
Madras. 

b. Central Museum. 
a. Observatory. 
Roorkee. 
p. Roorkee College. 
Ireland. 
Armagh. 

a. Observatory. 
Belfast. 

ab. Queen's College. 
Cork. 
p. Philosophical Society. 
ab. Queen's College. 
Dublin. 

a. Observatory. 
ab. National Library of Ireland. 
B. Royal College of Surgeons in Ireland. 
ab. Royal "Dublin Society. 
ab. Royal Irish Academy. 
Galway. 
ab. Queen's College. 



Italy. 

Acireale. 

p. Accademia di Scienze, Lettere ed Arti. 
Bologna. 

ab. Accademia delle Scienze dell' Istituto. 
Catania. 

ab. Accademia Gioenia di Scienze Naturali. 
Florence. 

p. Biblioteca Nazionale Centrale. 

ab. Museo Botanico. 

p. Reale Istituto di Studi Superiori. 
Genoa. 

p. Societa Lig-ustica di Scienze Naturali e 
Geografiche. 
Milan. 

ab. Reale Istituto Lombardo di Scienze, 
Lettere ed Arti. 

ab. Societa Italiana di Scienze Naturali. 
Modena. 

p. Le Stazioni Sperimentali Agrarie Italiane. 

Naples. 

p. Societa di Naturalisti. 

ab. Societa Reale, Accademia delle Scienze. 

b. Stazione Zoologica (Dr. Dohrn). 
Padua. 

p. University. 
Palermo. 

a. Circolo Matematico. 

ab. Consiglio di Perfezionamento (Societa di 
Scienze Naturali ed Economiche). 

a. Reale Osservatorio. 

Pisa. 

p. II Nuovo Cimento. 

p. Societa Toscana di Scienze Naturali. 
Rome. 

p. Accademia Pontiflcia de' Nuovi Lincei. 

p. Rassegna delle Scienze Geologiche in Italia. 

a. Reale Ufficio Centrale di Meteorologia e di 
Geodinamica, Collegio Romano. 

ab. Reale Accademia dei Lincei. 

p. R. Comitato Geologico d' Italia. 

a. Specola Vaticana. 

ab. Societa Italiana delle Scienze. 
Siena. 

p. Reale Accademia dei Fisiocritici, 
Turin. 

p. Laboratorio di Fisiologia. 

ab. Reale Accademia delle Scienze. 

Venice. 
p. Ateneo Veueto. 

ab. Reale Istituto Veneto di Scienze, Lettere 
ed Arti. 



r * ] 



Japan. 
Tokio. 

ab. Imperial University. 
p. Asiatic Society of Japan, 
Java. 

Buitenzorg. 

p. Jardin Botanique. 
Luxembourg. 
Luxembourg. 
p. Societe des Sciences Naturelles. 
Malta. 

p. Public Library. 
Mauritius, 

p. Royal Society of Arts and Sciences. 
Netherlands. 
Amsterdam. 

ab. Koninklijke Akadeuiie van Wetenscbappen. 
p. K. Zoologisch Genoofsehap ' Natura Artis 
Magistra.' 
Delft. 

p. Boole Polytecknique. 
Haarlem. 

ab. Hollandsche Maatschappij der Weten- 

schappen. 
p. Musee Teyler. 
Leyden. 

ab. University. 
Rotterdam. 

ab. Bataafscli Genc.-tschap der Proefonder- 
vindelijke Wijsbegeerte. 
Utrecht. 

ab. Provinciaal Genootschap van Kunsten en 
Wetenscbappen. 
New Brunswick. 
St. John. 
p. Natnral History Society. 
New Zealand. 
Wellington, 

ab. New Zealand Institute. 
Norway. 
Bergen. 

ab. Bergenske Museum. 
Christiania. 

ab. Kongelige Norske Frederiks Universitet. 
Tromsoe. 

p. Museum. 
Trondhjem. 

ab. Kongelige Norske Videnskabers Selskab. 
Nova Scotia. 
Halifax. 

p. Nova Scotian Institute of Science. 
Windsor. 

p. King's College Library. 



Portugal. 

Coimbra. 

ab. Universidade. 
Lisbon. 

ab. Academia Real das Sciencias. 

p. Seccao dos Trabalhos Geologicos de Portugal . 
Oporto. 

p. Annaes de Sciencias Naturaes. 
Russia. 
Dorpat. 

ab. Universite. 
Irkutsk. 

p. Societe Imperiale Russe de Geographie 
(Section de la Siberie Oi'ientale). 
Kazan . 

ab. Imperatorsky Kazansky Universitet. 
Kharkoff. 

p. Section Medicale de la Societe des Sciences 
Experimentales, Universite de Kharkow. 
Kieff. 

p. Societe des Naturalistes. 
Moscow. 

ab. Le Musee Public. 

B. Societe Imperiale des Naturalistes. 
Odessa. 

p. Societe des Naturalistes de la Nouve'le- 
Russie. 
Pulkowa. 

a. Nikolai Haupt-Sternwarte. 
St. Petersburg. 

ab. Academie Imperiale des Sciences. 

b. Archives des Sciences Biologiques. 
ab. Comite Geologique. 

p. Compass Observatory. 

A. Observatoire Physique Central. 
Scotland. 
Aberdeen. 

ab. University. 
Edinburgh. 

p. Geological Society. 

p. Royal College of Physicians (Reseai'ch 
Laboratory). 

p. Royal Medical Society. 

a. Royal Observatory. 

p. Royal Physical Society. 

p. Royal Scottish Society of Arts. 

ab. Royal Society. 
Glasgow. 

ab. Mitchell Free Library. 

p. Natural History Society. 

p. Philosophical Society. 
Servia. 
Belgrade. 

p. Academie Royale de Serbie. 



XI 



] 



Sicily. (See Italy.) 
Spain. 
Cadiz. 

A. Instituto y Observatorio de Marina de San 
Fernando. 
Madrid. 

p. Comision del Mapa Geologico de Espana, 

ab. Real Academia de Ciencias. 
Sweden. 
Gottenburg. 

ab. Kong] . Vetenskaps och Vitterhets Sainhalle. 
Lund. 

ab. Universitet. 
Stockholm. 

a. Acta Matheniatica. 

ab. Kongliga Svenska Vetenskaps-Akademie. 

ab. Sveriges Geologiska Undersokning. 
Upsala. 

ab. Universitet. 
Switzerland. 
Basel. 

p. Naturforschende Gesellschaft. 
Bern. 

AB. Allg. Schweizerische Gesellschaft. 

p. Naturforschende Gesellschaft. 
Geneva. 

AB. Societe de Physique et d'Histoire Naturelle. 

ab. Institnt National Genevois. 
Lausanne. 

p. Societe Vaudoise des Sciences Naturelles. 
Neuchatel. 

p. Societe des Sciences Naturelles. 
Zurich. 

ab. Das Schweizerische Polytechnikum. 

p. Naturforschende Gesellschaft. 

p. Sternwarte. 
Tasmania. 
Hobart. 

p. Royal Society of Tasmania. 
United States. 
Albany. 

ab. New York State Library. 
Annapolis. 

ab. Naval Academy. 
Atistin. 

p. Texas Academy of Sciences. 
Baltimore. 

ab. Johns Hopkins University. 
Berkeley. 

p. University of California. 



United States (continued). 

Boston. 

ab. American Academy of Sciences. 
b. Boston Society of Natural History. 

A. Technological Institute. 

Brooklyn. 

ab. Brooklyn Library. 

Cambridge. 

AB. Harvard University. 

B. Museum of Comparative Zoology. 

Chapel Hill (N.C.). 
p, Elisha Mitchell Scientific Society. 

Charleston. 

p. Elliott Society of Science and Art of South 
Carolina. 
Chicago. 

ab. Academy of Sciences. 

p. Journal of Comparative Neurology. 

Davenport (Iowa). 

p. Academy of Natural Sciences. 

Ithaca (N.T.). 
p. Physical Review (Cornell University). 

Madison. 

p. Wisconsin Academy of Sciences. 
Mount Hamilton (California). 

A. Lick Observatory. 

New Haven (Conn.). 

ab. American Journal of Science. 

ab. Connecticut Academy of Arts and Sciences. 

New York. 

p. American Geographical Society. 

p. American Museum of Natural History. 

p. New York Academy of Sciences. 

p. New York Medical Journal. 

p. School of Mines, Columbia College. 

Philadelphia. 

ab.- Academy of Natural Sciences. 
ab. American Philosophical Society. 
p. Franklin Institute. 
p. Wagner Free Institute of Science. 

Rochester (N.Y.). 

p. Academy of Science. 
St. Louis. 

p. Academy of Science. 
Salem (Mass.). 

p. American Association for the Advance- 
ment of Science. 

ab. Essex Institute. 

San Francisco. 

ab. California Academy of Sciences. 



[ xii J 



United States (continued). 
Washington. 

ab. Patent Office. 

ab. Smithsonian Institution. 

ab. United States Coast Survey. 

b. United States Commission of Fish and 

Fisheries. 
ab. United States Geological Survey. 



United States (continued). 
Washington (continued). 

ab. United States Naval Observatory. 
p. United States Department of Agriculture. 
a. United^ States Department of Agriculture 
(Weather Bureau). 
West Point (N.T.) 

ab. United States Military Academy. 



V 






CONTENTS. 



(A) 



VOL. 186.— PART T. 



I. On the Newtonian Constant of Gravitation. By C. V. Boys, A.R.S.M., F.R.S., 

Assistant Professor of Physics, Royal College of Science, South Ken- 
sington P a g e 1 

II. On the Photographic Spectrum of the Great Nebula in Orion. By J. Norman 

Lockyer, C.B., F.R.S. 73 

III. Propagation of Magnetization of Iron as affected by the Electric Currents in 

the Iron. By J. Hopkinson, F.R.S. , and E. Wilson 93 

IV. On the Dynamical Theory of Incompressible Viscous Fluids and the Determination 

of the Criterion. By Osborne Reynolds, M.A., II. D., F.R.S., Professor of 
Engineering in Owens College, Manchester 123 

V. On a Method of Determining the Thermal Conductivity of Metcds, with 

Applications to Coppjer, Silver, Gold, and Platinum. By James H. Gray, 
M.A., B.Sc, late " 1851 Exhibition" Scholar, Glasgow University. Commu- 
nicated by lord Kelvin, P.R.S. 165 

VI. Argon, a New Constituent of the Atmosphere. By lord Rayleigh, Sec. R.S., 

and Professor "W illi am Ramsay, F.R.S. 187 

jldcccxcv. — a. c 



[ xiv ] 

VII. On the Spectra of Argon. By William Crookes, F.R.S., &c. . . page 243 

VIII. The Liquefaction and Solidification of Argon. By Dr. K. Olszewski, Pro- 
fessor of CJiemistry in the University of Cracow. Communicated by Professor 
William Kamsay, F.R.S 253 

IX. TJie Latent Heat of Evaporation of Water. By E. H. Griffiths, M.A., 

Sidney Sussex College, Cambridge. Communicated by R. T. Glazebrook, 
F.R.S. 261 

X. Contributions to the Mathematical Theory of Evolution. — II. Skew Variation in 

Homogeneous Material. By Karl Pearson, University College. London. 
Communicated by Professor Henrici, F.R.S. 343 

XL A Determination of the Specific Heat of Water in Terms of the Lnternational 
Elective Units. By Arthur Schuster, F.R.S., Langxvorthy Professor of 
Physics at the Owens College, Manchester, and William Gannon, M.A., 
Exhibition (1851) Scholar, Queen's College, Gahvay 415 

XII. 7he Oscillations of a Rotating Ellijisoidcd Shell containing Fluid. By S. S. 

Hough, B.A., St. John's College, Cambridge. Communicated by Sir Robert 
S. Ball, F.R.S. 469 

XIII. On the Velocities of the Tons. By W. C. Dampier Whetham, M.A., Fellow of 

Trinity College, Cambridge. Communicated by Professor J. J. Thomson, 
F.R.S. 507 

XIV. On the Singular Solutions of Simidtaneous Ordinary Differential Equations 
and the Tlieory of Congruencies. By A. C. Dixon, M.A., Fellow of Trinity 
College, Cambridge, Professor of Mathematics in Queen's College, Gal way. 
Communicated by J. W. L. Glaisher, So.D., F.R.S. 523 

XV. On the Ratio of the Specific Heats of Some Compound Gases. By J. W. 

Capstick, M.A., D.Sc, Fellow of Trinity College, Cambridge. Communicated 
by Professor J. J. Thomson, F.R.S. = . . 567 

XVI. Iron and Steel at Welding Temperatures. By T. Wrightson, M.P., Memb. 

List. C.E. Communicated by Professor Roberts- Austen, C.B., F.R.S. 593 

Index to Part I. 



LIST OF ILLUSTRATIONS. 

Plates 1 and 2. — Professor C. V. Boys on the Newtonian Constant of Gravitation. 

Plate 3. — Mr. William Crookes on the Spectra of Argon. 

Plates 4 to 6. — Mr. E. H. Griffiths on the Latent Heat of Evaporation of Water. 

Plates 7 to 16. — Mr. K. Pearson on the Mathematical Theory of Evolution.— II. 
Skew Variation in Homogeneous Material. 

Plate 17. — Mr. T. Wrkhtson on Iron and Steel at Welding Temperatures. 



PHILOSOPHICAL TRANSACTIONS. 



I. On the Newtonian Constant of Gravitation. 

By C. V. Boys, A.R.S.M., F.R.S., Assistant Professor of Physics, Royal College of 

Science, South Kensington. 



Received May 31, — Read June 7, — Revised October 18, 1894. 

[Plates 1, 2.] 
Table of Contents. 

1'AGE, 

Part I. (pp. 1 to 37). 

Preliminary 1 

The apparatus ■ 8 

The laboratory and accessories 12 

The large scale 14 

The overhead pnllies 15 

The steel tape and its accessories 17 

The optical compass 18 

The small glass scale 20 

The clock 24 

The large balls and their supports 25 

The small balls or cylinders 29 

The beam mirror and its attachments 31 

Conclusion of Part 1 37 

Part II. (pp. 37 to 5<J). 

Part III. (pp. 51 to 71). 

The deflections and periods 51 

The geometry of the apparatus 56 

The dynamics of the moving system 59 

The combination of the preceding three results 61 

Conclusion 69 

MDCCCXCV. — A. I! 5.3.95. 



2 PROFESSOR C. V. BOYS ON THE 

P^RT I. 

Preliminary. 

In a paper on the Cavendish experiment, published in the ' Proc. Roy Soc.,' vol. 46, 
p. 253, I showed how the famous experiment of Cavendish* could be transformed in 
several particulars, so that greatly increased delicacy and accuracy would be obtainable. 

The experiment is so well known that there is no occasion to describe the apparatus 
which Cavendish employed, or the subsequent work of Reich, t Baily,| or Cornu 
and Bailee. § It is sufficient to state that, owing* to the extremely small value of the 
Newtonian constant of gravitation, all these experimenters made use of balls as large 
as they conveniently cordd, so as to increase the force of attraction as much as 
possible, and of a lever as long as they could, so as to increase the effect of the force 
in producing torsion. However, Corntj realized that if he could keep the period the 
same by the use of a sufficiently fine torsion wire, and reduce the dimensions of the 
whole apparatus, the angle of deflection would not be reduced but would remain the 
same. Cornu also introduced refinements which have made the behaviour of his 
apparatus far more consistent than that of any which had preceded it. 

Soon after I had made and found the value of quartz fibres for producing a very 
small and constant torsion, I thought that it might be possible to apply them to the 
Cavendish apparatus with advantage, which opinion I found was also held by 
Professor Tyndall. Before employing them for this purpose I examined the theory 
of the apparatus with a view to using them in the most suitable manner. 

The sensibility of this kind of apparatus is, if the period is maintained always the 
same, independent of its linear dimensions ; for in two similar instruments, in which 
all the dimensions of one are n times the corresponding dimensions of the other, the 
moments of inertia of the beams and their appendages are as n 5 : 1 , and, therefore, if the 
period is to be unchanged, the torsional couples must be as n 5 : 1 also. The attracting 
masses, both fixed and movable, are as n 3 : 1, and their distances apart asn: 1 ; there- 
fore, the attentions are as ?i 6 /?i 2 , or asn*: 1, and these, acting on arms n times as long 
in one as in the other, produce moments as n 5 : 1 ; that is, in the same proportion as 
the torsional rigidities, and so the angles of deflection are the same in the two cases. 

If, however, the length of the beam only is changed, and the attracting masses are 
moved until they are opposite to and a fixed distance from the ends of the beam, then 
the moments of inertia will be altered in the ratio n 2 : 1, while the corresponding 
moments will only change in the ratio n : 1, and thus there is an advantage in 
reducing the length of the beam until one of two things happens, either it is difficult 
to find a sufficiently fine torsion thread that will safely carry the beam and produce the 
required period — and this, no doubt, has prevented the use of a beam less than that 

* ' Phil. Trans.,' 179S, p. 469. 

t ' Comptes Rendus,' 1837, p. 697. 

t ' Phil. Mag.,' vol. 21, 1842, p. 111. 

§ ' Comptes Rendus,' vol. 76, p. 954; vol. 86, pp. 571, 699, 1001. 



NEWTONIAN CONSTANT OF GRAVITATION. J 

half a metre in length — or else, when the length becomes nearly equal to the diameter 
of the attracting balls, they then act with such an increasing effect on the suspended 
balls at the other end of the beam, that the balance of effect begins to fall short of that 
which would be due to the reduced dimensions if the opposite ball did not interfere. 

I showed, in the paper already referred to, that when the attracting balls have been 
brought as near to the equatorial plane, or plane perpendicular, to the. length of the 
beam, as they are to the plane of the beam, so that the line joining them makes an 
angle of 45° with the beam, that is that the azimuth is 45°, the ultimate sensi- 
bility is still further increased by shortening the beam to half the length that would 
bring the ends opposite the attracting balls. After that the sensibility very slowly 
begins to fall. 

Since, with such small apparatus as the quartz fibre seemed to make practicable, it 
is easy to provide attracting masses which are very large in proportion to the length 
of the beam, while with the usual long beam relatively small masses must be made 
use of, it is clear that much greater deflections can be produced with small than with 
large apparatus. For instance, to obtain the same effect in the same time in an 
instrument with a 6-foot beam that I was able to realize in my preliminary apparatus, 
in which the beam was ^ inch in length, as seen from above, with attracting balls 
2 inches in diameter, it would be necessary to provide and deal with a pair of balls 
each 25 feet in diameter, and weighing 730 tons, instead of about If lb. apiece. 
There is the further advantage in small apparatus that if, for any reason, the greatest 
possible effect is desired, attracting balls of gold would not be entirely unattainable. 

The use of attracting balls which are themselves very large compared with the 
beam length makes it convenient to hang the beam in a cylindrical tube, instead of in 
the long box almost universally employed hitherto. Several advantages follow from 
this. In the first place, if the beam is hung centrally, neither the gravitational 
attraction of the tube nor any minute difference of potential between the tube and the 
beam and its accessories, produce any effect. In the second place, the attracting balls 
may be carried round outside the tube through a complete circle, and yet be placed 
but little further from the attracted balls than would be necessary if no intervening 
tube existed. For this purpose they are conveniently supported by a common 
metallic structure, symmetrical in form, about the axis of the tube, and able to rotate 
about this axis also. If, following the usual arrangement, all four balls are on one 
level, there are obviously two planes, one containing and one normal to the beam, in 
which the centres of the attracting balls may be placed so as to produce no deflection. 
At some intermediate position the deflection will be a maximum. The use of this 
position has the obvious advantage that, besides the fact that this gives the greatest 
effect, the accuracy with which the angle of azimuth is measured is of little conse- 
quence, the geometrical measurements of real importance being the distance between 
the centres of the large balls, the corresponding distance between the centres of the 
small balls, and the angle of deflection. This is all the more important since it would 
be extremely difficult to make a really accurate determination of the azimuth, 

B 2 



4 PROFESSOR C. V. BOYS ON THE 

whereas the other three quantities can be measured, as will appear later, with the 
highest degree of precision. 

It will be evident that, as the size of the attracting balls is increased with the 
object of increasing the deflection, their action on the opposite suspended balls increases 
in a very high ratio, so that very soon a practical limit is reached, beyond which any 
increase of size produces an insignificant effect. For instance, if the distance between 
the centres of the attracting balls is five times the length of the beam, and they are 
set at the angle (58° 20') at Avhich their action is a maximum, the counteracting 
couple due to the far ball is |- of that due to the near one, so that the resultant couple 
is only f of that which would be produced if the attraction on the remote end of the 
beam could be annulled. This, in effect, I practically accomplished by arranging the 
two sides of the apparatus at very different levels. In this way, if only the exact 
position of the balls can be determined, or rather their co-ordinates can be ascertained 
with degrees of accuracy in proportion to their importance, then the arrangement is 
eminently suitable for the purpose of finding the gravitation constant. 

The preliminary apparatus that I made on this principle in 1889 worked so well, 
even under the unfavourable conditions met with at South Kensington, that I felt 
satisfied that an instrument built on the same lines, but in which the necessary 
geometrical measurements could be made, would enable me to make a more accurate 
measure of the Newtonian constant than had been considered possible hitherto. I 
even felt satisfied that it could be determined with an accuracy of 1 in 10,000 ; and 
this extreme degree of precision I now feel certain may be attained by a skilled 
experimentalist, if the very small modifications suggested by my recent work, which 
are described at the end of this paper, are adopted, and if, above all, the experimen- 
talist,- whoever he may be, has time and place at his command, and is not driven by 
necessity to steal as much time for observation from his holidays and nights as his 
physical strength will allow. 

In the design of any apparatus, it is necessary to have some definite idea as to the 
degree of accuracy which is to be aimed at, so that trouble may not be taken in 
attaining an absurd degree of precision in one part, while some other part is glaringly 
in defect. The aim which I made, and which my preliminary experiments showed 
to be reasonable, was one of 1 in 10,000 in the result ; for this purpose the large 
masses would have to be determined 







to 


1 


in 


10,000; 




times 


?? 


1 


3> 


20,000 ; 


some 


lengths 


3J 


1 


33 


20,000 about ; 


other 


? j 


?3 


1 


33 


10,000 „ ; 




in angle 


JJ 


1 


33 


10,000. 



I gathered from conversation with some physicists of note, whose judgment and 
experience I fully appreciated, that there was some doubt whether I was doing right 
in persisting in making small apparatus where absolute determinations were the 
object, for though I had clearly enough shown that so far as sensibility and constancy 



NEWTONIAN CONSTANT OF GRAVITATION. 5 

of deflection and period were concerned an advantage could jso be obtained, it did not 
at all follow that I should be able to determine the geometry of small apparatus with 
sufficient accuracy. Of course, as the apparatus is made smaller, this difficulty 
necessarily increases. 

If in the apparatus upon which I have finally decided the angular deflections and 
squares of the periods can be determined with greater proportionate accuracy than 
the masses or lengths, or lengths squared, as the case may be, then I have gone too far, 
and the apparatus is too small, but if, as I expect to satisfactorily prove in this paper, 
my geometry and weighings (of course, the latter) are well in excess of the 
deflections and squares of the periods in point of accuracy, then I maintain that I am 
justified in having acted up to my principles, even though I did so in opposition to 
the views which I heard expressed. 

There is one point referred to (p. 258), but not sufficiently in detail, in my paper 
already quoted which I should like to develope, more especially as Professor Poynting* 
has noticed it, and has, I think, agreed with my conclusion. At the same time I owe 
to him the discovery of a mistake which I made which led me to attribute too high an 
importance to the advantage of smallness from this point of view. What follows is 
the result of a discussion, which I took the opportunity of entering upon while 
travelling recently with Professor Poynting. The point is, that the disturbances 
due to convection are likely to be relatively of less importance in small than in large 
apparatus, even though the period is maintained the same. As convection disturb- 
ances are those which are the last and the most difficult to avoid, and as I feel sure 
that they set the limit to the accuracy that is obtainable in this experiment, and that 
discrepancies attributed to silk, or even to quartz fibres, and to other causes, are in 
many physical investigations simply due to convection, I think that too much 
attention cannot be given to this part of the subject. 

Let there be two pieces of apparatus, precisely similar in all respects, but with the 
linear dimensions in one n times those in the other, then when the pieces of 
apparatus are set up, they are subject under the best conditions to infinitesimal 
variations of temperature from the outside of two kinds ; in the first, the surrounding 
space may not be uniform in temperature, it may be hotter on one side than on the 
other ; in the other, the temperature, whether uniform or not, may slowly change 
from day to day. 

In the first case the instruments ma}?' be considered as being placed in a region 
which would, but for their existence, possess a constant but very small tempei'ature 
gradient. If an instrument be placed in such a region, the temperature gradient in 
the instrument will be also constant in certain cases, and will depend simply on the 
conductivity for heat of the material of which it is made and of the medium in which 
it is placed, but it will be independent of the linear dimensions. Further, whatever 
form a pair of similar instruments may have, the gradients at corresponding points in 

* 'Phil. Trans.,' 1892, vol. 182, p. 601, and "The Mean Density of the Earth," p. 107. 



6 PROFESSOR C. V. BOYS ON THE 

each will be independent of the linear dimensions, and so the temperature differences 
of coi'responding pairs of points or of the two sides will be proportional to ft. In con- 
sequence of this difference of temperature the included air will be warmer on one side 
than on the other and will circulate. The linear velocity of circulation will depend 
upon the difference of pressure between the ends of the upcast and downcast sides 
divided by the resistance due to viscosity, i.e., in such cases as we are concerned with, 
where the pressures and velocities are infinitesimal, and practically all the energy is 
expended in overcoming viscosity and none in imparting energy of motion to the gas. 

The difference of pressure varies as the height multiplied by the difference of tem- 
perature, or as n" : 1. The effect of viscosity is proportional to the length of the 
channel, and inversely as its area; it varies, therefore, as ft -1 : 1. The velocity of 
circulation will vary as n 2 /n~ J , or as n 3 : 1. In order to ascertain what disturbing 
effect this movement may have upon the suspended part of the apparatus, we may 
either consider that the force depends upon the product of the area into the velocity 
gradient or rate of shear of the surrounding air, i.e., that it is proportional to ft 3 X ft a , 
or ft 4 , in which case, since the force is to be multiplied by an arm also n times as long 
in order to obtain the couple, this becomes n s ; or without considering the velocity at 
all we may consider the suspension as part of the boundary of the gas receiving its 
share of the drag which is felt by the surrounding tube. The proportion must be the 
same in the two cases. The force causing the drag is proportional to the difference in 
temperature of the air columns multiplied by their area, or to ft 4 , and, therefore, the 
drag on the suspension varies as ?i* and the couple produced as n 5 , as before. From 
this it would apj:>ear that no gain or loss results from a diminution of size. It must, 
however, be remembered, that, as apparatus is made lai'ger, the three-fold increase in 
velocity in the air-current may well bring it up to such a value that its square can no 
longer be considered inappreciable. When the velocity is sufficient for the effect of 
impact to be felt, then the couple will follow a law depending upon a higher power 
of ft than the fifth which, with increase of velocity, will approach the eighth power of 
the linear dimensions. 

I do not anticipate with my design, which with its double tube and protecting 
screens is eminently favourable for the attainment of a uniform temperature in the 
inside, that the ah velocity will ever approach that in which the square becomes 
appreciable, so that in a suitable underground observing room I should not expect any 
loss of definiteness to follow a moderate increase of size ; nevertheless, I should feel 
doubtful as to the result if the dimensions were increased inordinately. Practically, 
however, smallness has a very great advantage, owing to the length of time which 
must elapse between the carrying out of any operation in which the apparatus is 
handled or otherwise warmed b}- manipulation, and its acquiring such a steady state 
again as to be fit for the observer to make the delicate observations of the movements 
of the susjDended system. I have even considered three days to be necessary for my 
small apparatus to be ready for observation of deflection and period after making the 



NEWTONIAN CONSTANT OF GRAVITATION. 7 

micrometric observation. This, in fact, corresponds, but not exactly, with the second 
case mentioned above, where a gradual change of temperature is going on in the 
surrounding space ; those parts of the apparatus that are massive will lag behind in 
temperature more than the lighter and thinner parts, and, as was pointed out by 
Cavendtsh, this is especially the case in apparatus for measuring the Newtonian 
constant of gravitation. The large lead balls are sure to be hotter or cooler than the 
light rectangular box, and, when hotter, by warming the side of the box near to 
them they set up a circulation, which, in the apparatus of Cavendish, produced an 
appearance of attraction. 

Jf it is supposed that after all has acquired a uniform temperature a slight change 
occurs in the surrounding space, then the asymmetrical store of heat will, in the 
case of a large apparatus, be n 3 times as great as in the other. As before, the 
conductivity will be n times as great, so that an asymmetrical distribution of 
temperature will be n times as great, and will last n times as long in the large as in 
the small apparatus. 

Before I come to describe the apparatus which forms the subject of the present 
paper, I wish to explain why I have employed what may appear objectionable, viz., 
mixed units. I applied to Mr. Chaney, at the Standards Office, for his opinion,, as 
to the limit of accuracy with which he could verify certain lengths and masses. The 
lengths upon which the accuracy of the whole research would depend were to be of 
the order of 1 inch and 6 inches. If I could, as he considered certain, have them 
determined more accurately in relation to the standard 1-inch than I could in 
relation to the centimetre, it would be preferable to have the main dimensions of 
the apparatus set out in terms of the inch, and for construction in England there 
were practical advantages in adopting the inch system. On the other hand, the 
cathetometer that I used (Cambridge Scientific Instrument Co.'s), and the screw 
micrometer (Elliot), both of which were required to make measures of only 
secondary importance, were divided in centimetres. I have therefore had to make 
use of both kinds of measures, but have retained the inch as my standard. With 
respect to the masses, no difficulty could arise in obtaining the necessary accuracy, 
whether pounds or grammes were used. Having gramme weights I was led to 
make all the weighings in grammes, except where, owing to an insufficiency, I 
had to make up with a standard 7 lb. and 4 lb. weight belonging to the South 
Kensington Museum. These were determined in grammes, and expressed as such. 
Circumstances have therefore compelled me to carry out my experiments on the 
inch gramme second system, and this I have done, finally converting the values 
for G so found into the C.G.S. system, by multiplying by the number of cubic 
centimetres in a cubic inch. (2-53995) 3 = 16-3861. 

As the suspended masses take up slightly different positions according as they are 
attracted by the large balls in one or the other direction, I was most careful in the 
design to arrange that the apparatus, with the exception of these balls, should be one 



8 PROFESSOR C. V. BOYS ON THE 

figure of revolution about the suspending fibre as an axis. With the hope of obtaining 
very perfectly conducting and uniform cylinders, both for the outer case and for the 
central tube, I ascertained what sizes of Elmore tube would be obtainable, and thus 
determined the actual and final dimensions of the apparatus. When this was too 
far advanced for change to be possible, the Elmore Company informed me that they 
could not supply the sizes previously settled, and so I had to be content with a piece 
of thick triblet-drawn brazed copper tube for the centre, and a thick brass casting 
for the surrounding case. The experiments show that no appreciable disturbance has 
arisen owing to any want of perfection in the tube. The casting was turned inside and 
out without being moved from the face plate, and, except in conductivity, is as perfect 
as pure copper. In order to keep the gravitational symmetry round the axis as perfect 
as possible, I had holes dialled in the massive base round the levelling screws, so as to 
remove as much metal as they added. The important dimensions on which I finally 
decided were : — 

Distance from centre to centre of large balls in plan, 6 inches or 4 inches. 

Distance from centre to centre of small balls in plan, 1 inch, about. 

Diameter of large balls, 4|- inches or 2\ inches. 

Diameter of small balls, "2 inch and '25 inch. 

Difference of level between upper and lower pairs, 6 inches. 

With these settled the rest of the design of the apparatus shown in figs. 1-15 
followed naturally enough. I think it most convenient first to describe the apparatus 
in moderate detail, without going into the reasons why I decided upon each particular, 
and afterwards to show how the design accomplishes all that is needed for an accurate 
determination of G, the Newtonian constant of gravitation. 

TJie Apparatus (Plate 1). 

Fig. 1 is a vertical section through the centre of the apparatus, the window alone 
being in elevation ; fig. 2 is a sectional plan through aa. Taking the structure first, 
B is a massive brass base, turned on both sides, carried by three levelling screws with 
lock nuts. C is the outer brass cylindrical casing screwed to the base B and accu- 
lately turned as already mentioned. L is a turned brass lid mechanically fitting C, 
on which it can be made to turn by the action of the train of wheels WWW. The 
edge of the flange is divided in degrees, and can be read to yq° upon the vernier V, 
fig. 3. Two tubular pillars PP are fitted into holes diametrically opposite to one 
another and 6 inches or 4 inches apart, according to the size of ball that is to be 
used. The heads of these pillars are shown half size in figs. 4, 5, 6, where it will 
be seen that at angles of 120° there are three radial V's forming a geometrical clamp 
with either ball support. Also that on just raising the latter and giving it a rotation 
of 60° it can be let down through the tubular pillar. As seen, the large balls hang 
from these geometrical clamps by wires, but into these particulars and into the details 



NEWTONIAN CONSTANT OF GRAVITATION. 9 

connected with the construction of the balls I shall enter later. The central tube T 
is held accurately in its place by a cylindrical fitting and the hollow screw S. This 
tube, up to the window just above the lid, is made of thick copper ; at the window 
level it is united by the window casting to the upper tube of the same size, which is 
made of brass, and this carries at its upper end the torsion head surmounted by the 
bell jar J with a central stop-cock. The torsion head admits of a variation of level 
of about 2 inches and of horizontal adjustment by msans of three screAvs. The 
window casting forming the centre of the tube does not touch the lid, there being a 
space of about -^j of an inch between them. The equality of this all round is 
an excellent test of the accuracy of this part of the construction. The window is 
shown half size in figs. 8, 9, and 10. Fig. 8 is a front view, the upper part being in 
section, fig. 9 is a side view, and fig. 10a section through aa. The thick cylindrical 
casting is cut through front and back so as to form two flat square faces FF 2 inches 
in the side each, and over these 2 inches the casting is cut right through, forming 
a square chamber in which the beam mirror hangs, and certain operations can be 
carried on. Four milled heads h u h. 2 are employed in making the transfer of the 
smaller balls to and from the beam mirror, of which an enlarged view is shown in 
fig. 7. This operation is performed as follows : the two heads h i are fixed to 
the same cross axle, and when turned through a right angle cause two arms 
with V notches at their ends to pick up the beam (fig. 7) by its upper cross 
arms. In this way the beam can be raised or lowered a little or let down so 
as to hang from its torsion fibre. The small balls hang by quartz fibres from the 
hooks and eyes seen in fig. 7. When not on the beam these hang by their eyes from 
the points projecting from the cranked ends of the pins operated by the heads h. 2 h 2 , 
which can be turned or pushed in or drawn out. By combining the movement of 
the heads h x and h 2 one of the hooks and eyes can be transferred to the V at the end 
of the upper arm of the beam mirror resting there by its hook. In the same way 
the other one is transferred. To prevent risk of the tipping of the beam and 
fracture of the torsion fibre during this operation, a weight is first hung on to the 
lower central hook of the beam and removed when the double operation is complete. 
The ends of the mirror have very fine V grooves ground in them, so that the quartz 
fibres hanging from the hooks may lie in these grooves and so be held definitely in 
position, both with respect to their distance apart and circumferentially with 
respect to the mirror. A cylindrical counter-weight K, fig. 7, of known very small 
moment of inertia, but of exactly the same weight as the small balls with their hooks 
and fibres, can be hung upon the central hook of the beam, when the balls are 
removed to the side hooks, so that the fibre may be stretched to the same extent 
and therefore have the same torsional rigidity when the periods are being taken with 
or without the small pair of balls. 

A series of windows are provided to fit upon and make an air-tight joint with the 
plane-faces F F. Two are mere squares of plate-glass of the exact size needed. These 

MDCCCXCV. — a. c 



10 PROFESSOR C. V. BOYS ON THE 

are used to protect the freely hanging mirror from draughts when observations are 
made upon it with the cathetometer. The window, fig. 11, is made of brass, electro- 
gilt, with a small aperture just large enough to allow the telescope T, figs. 18, 19, 
and all parts of the scale S, figs. 18, 21, to be seen from all parts of the mirror. The 
outer face of this window is covered with a plate of glass optically worked by Hilger, 
held in place by soft wax. The top and bottom sectors and the faces F F are smeared 
with vaseline to make an air-tight joint when the window is in position. The 
window, fig. 12, is made of brass, electro-gilt ; it is similarly fixed in position behind 
the mirror. A brass tube, lightly filled with cotton-wool, screws into this window on 
one side. The window shown in vertical section, fig. 13 and in plan, fig. 14, is made 
of brass with a flat tubular opening with rounded ends. This enters the rectangular 
chamber and rests against the faces F F, which have been cut away ab their lower 
part sufficiently for this purpose. The inner end of this tube is covered with a 
naturally cleaved thin film of mica, which enables the two quartz fibres hanging from 
the freely suspended mirror to be seen by two high-power microscopes whose noses 
penetrate into the flat tube without allowing them to be blown about by draughts. 
The use of mica for this purpose is essential. Mr. Cunynghame had previously 
shown me that the definition of a good telescope, which is absolutely destroyed by 
window glass held in front of it and impaired by any but perfect optically worked 
glass, is not affected by a leaf of mica, even though it may be bent or be apparently 
irregular. In the same way, the apparent position of anything seen by a microscope 
is altered if a piece of ordinary cover glass is placed between the two at some distance 
from the object, besides which the definition suffers. A thin leaf of mica in no way 
affects the definition or the apparent position, and so the distance apart of the fibres 
measured by the microscopes, as will be described later, is the true distance, which it 
never would be if cover glass were employed. This distance must be measured with 
the mirror freely hanging so that it may be the same as it is when the deflections, etc., 
are being observed. 

Resting on the base B, fig. 1, are four india-rubber discs I R, with large central 
holes, their object being to form a soft cushion for the lead balls MM to rest upon 
when not suspended or to fall upon in case of accident. 

In the same way I have provided a safety catch and recovering device in case the 
small balls should fall down the central tube. When the mirror is suspended and 
has been adjusted with its torsion fibre axial, the loss of time that would ensue if 
the little balls could only be recovered by moving the central tube is so great that 
some contrivance of the kind is necessary. At first I merely had some cotton-wool 
at the bottom of the tube, and fished for the little balls with an india-rubber tube 
let down through one window opening. On sucking air through the end with the 
mouth, the balls could generally be picked up and drawn out attached to the lower 
end of the pipe. My present plan is less precarious. W is a piece of wood loosely 
fitting the tube. On this there is half an inch or so of cotton-wool on which is a disc 



NEWTONIAN CONSTANT OF GRAVITATION. 11 

of wash-leather just fitting the tube. A piece of thread long enough to reach beyond 
the window is fastened at one end to the piece of wood and at the other end to a 
small fragment of iron wire. The thread and wire rest upon the wash-leather, and 
to make sure of this a second cylinder of wood is let down to press all in place. In 
case of' accident to the little balls, a magnetized tuning-fork is let down the tubes by 
a piece of string, and the iron wire pulled up. It is then easy, by pulling the thread, 
to bring the wash-leather to the window level and so to pick out the little balls with 
forceps, 

Fig. 15 is a vertical section of the innermost of the series of screens employed to 
protect the apparatus from variations of temperature. I could not at first believe that 
these would be required, but each additional protection of the kind has certainly 
improved the constancy of behaviour of the apparatus, and I have now no doubt as to 
the necessity for their use. t x is a brass tube with inner and outer ledges split into 
two halves, so as to fit on to the upper part of the window casting shown in chain 
lines ; t 2 is a plain brass tube reaching nearly to the top of the central tube, and t 3 is 
a third brass tube, with an internal ledge resting on t v This is large enough to 
clear the milled heads h v h. 2 . An opening is made in it large enough to allow the 
telescope T and all parts of the scale S to be seen from all parts of the mirror. There 
is also a small hole in the back, through which the tube of the window, fig. 12, can 
be screwed. The screen tube £ 3 is just clear of the lid and the window tube. 

To protect the whole instrument from variations in temperature it is completely 
surrounded by the octagon house, of which a horizontal section is shown in fig. 22. 
It is double-walled, and is made in two halves of f-inch pine boards, separated by a 
space of 1 inch. This is filled with cotton-wool. The top is flat, double, and packed 
with cotton-wool in the same way. The two halves slide together upon the table on 
which the instrument is placed, and meet, completely enclosing it, with the exception 
of a small hole in the centi'e of the top, through which a cord, the use of which will 
be described later, can pass ; of a narrow slit in the front, through which the scale 
and telescope may be seen from the mirror ; and of two small apertures through 
one of which the vernier V may be seen by the aid of the small telescope t (figs. 18, 
19), the other admitting of the driving wheel D and air tube. The connecting wire 
between D and the wheelwork above lies in the narrow space between the inner and 
outer boards and the two styles which separate them. 

By way of illustrating the state of steadiness to which I have reduced the air in 
the central tube, I may give the result of a calculation made in the case of Experi- 
ment 8. In that experiment the points of rest would have been disturbed by one 
unit if the air in the tube had been moving round at the rate of one turn in six weeks, 
i.e., at such a rate as to blow past the balls at a rate of 1 inch in 13-J days. This 
follows immediately from the torsional rigidity, decrement, period, and angular value 
of one division. No uncertainty so great as this appears in the mean deflections 
obtained during the night. 

C.2 



12 PROFESSOR C. V. BOYS ON THE 



The Laboratory and Accessories (Plate 2). 

The apparatus is set up in the vaults under the Clar-endon Laboratory at Oxford, to 
fit which, in fact, it was specially designed. I cannot sufficiently express ray obligation 
to Professor Clifton for giving up to me entirely for four years this very perfect 
observing ixiorn, for not only was I able to make my observations under specially 
favourable conditions, but I have had the advantage of having at hand the resources of 
his splendidly equipped laboratories, and of being allowed to make any use of them 
that I desired. I feel that Professor Clifton's kindness in the matter is the greater 
as I have no claim upon him whatever, and I can only hope that in so far as my work 
carried out in his rooms may represent progress in practical physics, he may feel 
justified in having sacrificed to this end his best observing quarters. 

The vault is a double one, of which the southern half is shown in plan in fig. 18. 
This is separated from the northern half by two piers. The entrance is by a door at 
the east end of the northern half. The two tables, A lt A 3 , which Professor Clifton 
had built for the purpose of the experiment in tbe positions shown, are of his standard 
pattern. The top, made of one slab of slate, rests on a large block of freestone, and 
this is supported by three walls of brick set in cement, forming an H. The instrument 
surrounded by the octagon house is placed upon the table A P On the table A 3 is 
arranged a large astronomical telescope T, by Cooke, of York, by means of which the 
scale is read by reflection from the mirror. The great focal length and the perfection of 
the object glass are necessary to obtain sufficient magnifying power to be able to read 
with certainty to -j^- s incn on ^ ne scale ; the large diameter of 4 inches has the 
advantage of giving a large field of view, which is almost essential in taking rapid 
transits. Moreover, telescopes of the same perfection of construction and length are 
not immediately obtainable of smaller diameter. This telescope is supported by two 
cast-iron standards, each with its own travelling V, of my own construction, which 
give absolute steadiness, being geometrically designed. In this way a considerable 
range of height can be obtained in case it is wanted. The small telescope t, for 
reading the vernier V, by which the angular position of the lid and of the large balls 
M M is determined, also stands on the table A 2 . Besides the telescopes, a pulley- 
wheel p x rests upon the table, and a driving-wheel d is clamped to it ; p l is pulled 
by a stretching weight, so as to keep the blind cord b passing round the other wheels 
■p. 2 , p 3 , and fastened to the go-cart g in a state of tension. The cart is a beautifully 
executed specimen of part of a " natural philosophy set " of the last century, and was 
lent me by Mr. G. S. New t th. It runs on the wooden framework, which is wedged into 
the recess at the east end of the room, between a pair of rails made of angle brass. It 
carries an albo-carbon lamp, so that the flame can be brought behind any division of 
the great scale S, which may be seen in the telescope T by reflection from the mirror. 
The flame is turned down very low to avoid heating the room unnecessarily. I 



NEWTONIAN CONSTANT OF GRAVITATION. 13 

generally set it so that the flame is about \ inch wide and \ inch high. The driving- 
wheel D is made with two heavy projections not shown in the figure, to give it con- 
siderable moment of inertia, and with the handle at a distance of an inch about from 
the axis. Any motion given to it by hand is therefore less likely to be subject to 
jerks than it would be if unweighted. A very light cord rests loosely round this 
pulley, is supported by an arm of wood projecting from the other end of the table, is 
supported again on the edge of the other table, and then lightly passes round the 
little wheel D, figs. 1 and 2. This rests upon the table, and is kept from moving 
about by a weighted foot. Two pins fastened into the wheel D engage in a hole and 
slot in the cross-piece y at the bottom of the hanging wire b. Thus when D is turned 
the motion is communicated to the wheel- work WWW through the light and loose 
cord, the wheel D, and the cross-arm and wire. The only kind of force between the 
wheel D and the wire is by the construction a couple, and this, owing to the high 
ratio of gearing in the wheel-work WWW, need be only very small to give motion to 
the lid L. The friction due to the great weight of the balls M M, and of the lid, is 
largely reduced by hooking to the two rods E, R screwed into the lid guys joined to a 
cross-bar above the bell-jar, which there hangs from a single line passing round the 
centre one of five wheels secured to the arch, the edge of this being exactly above the 
axis of the instrument. The line then passes over a second wheel close to the west 
wall of the vault, and carries two weights each exactly equal to one of the balls, and 
an extra weight to partly balance the weight of the lid. When the handle of the 
wheel d is turned the lid slowly and almost insensibly creeps round, and no tremor 
appreciable with ordinary apparatus is communicated to the suspended mirror. 
Owing to the extreme sensitiveness of the apparatus, and the very great magnifying 
power, a high period tremor is set up in the mirror, about equal in amount to that 
caused by ordinary traffic in St. Giles', about a quarter of a mile away. This dies 
away veiy rapidly, and I am unable to trace any anomaly to this cause. The corner 
of the vault, in which the instrument is placed, is screened off from such small 
variations in temperature as my presence and the small gas flame produce, by 
two double partitions of felt, f\f\,f%f^- Furthermore, the vault itself is protected 
from variations in the temperature of the air, in the long underground passage by 
which it is approached, by two felt curtains some distance apart. 

Slits and holes, no larger than are necessary, are made in the partitions fij\ to 
allow the scale and telescope T to be seen from the mirror, the vernier V to be seen 
from the telescope t and the light string to pass through. These partitions are 
temporarily lifted out of the way when a certain beam l v shown in position in fig. 19 
but not in fig. 18, is being used. The two beams l 1} l z have their upper edges planed 
true, and are so supported by levelling screws that their upper edges form one level 
straight edge. These are emplo} T ed when the distance from the scale to the mirror is 
being determined in the manner to be described under the heading " The Steel Tape 
and Accessories." The beam l 2 I leave in position permanently, but as l x would be in 
the way, it is only put up when required. 



14 PROFESSOR C. V. BOYS ON THE 



The Large Scale. 

The large scale is etched on a piece of plate-glass 9 feet long, 6 inches wide, and 
half an inch thick. The divisions are 50ths of an inch, and there are 4800 of them. 
I made many experiments to find the most suitable kind of scale and thickness of line 
to suit the mirror which I had to use. I shall return to this point when I explain 
the advantages that I have gained by the use of the curious form of beam mirror. It 
is sufficient to state now that the divisions are black upon a clear ground, and that 
the thickness of the lines is greater than at first anyone would be likely to think 
suitable, being about -^q of an inch. The method by which the scale is held rigidly 
and definitely in place but without strain, is illustrated by the isometrical projection 
in fig. 23, which shows one end only. Z Z are a pair of gun-metal castings screwed 
to the wood frame which is securely wedged into the recess at the east end of the 
vault, u is a brass rod passing through a hole in each casting and able to be 
clamped by a screw at each end. v is a casting with a cylindrical piece turned at 
each end and exactly the same length between shoulders as u is. This rests at each 
end upon a levelling screw, and can be clamped by pinching screws. At the other 
end of the scale, 9 feet away, there is an identical construction. Two plates of glass, 
the back one of which is a dummy, the front one only being divided, rest ujaon the 
cylindrical projections of v, being definitely held in position by the V notch shown, 
which of course is only at one end. The glass plates rest also against the shoulders 
and against the ends of u u and are kept in contact by the action of a bent piece of 
brass at each end which lightly presses them towards one another. The glass plates 
are therefore geometrically clamped, each resting on seven points, the one in excess 
of six being introduced to counteract the one degree of freedom which the flexure of 
so long a plate introduces. The middle of the front plate is silvered at the back up 
to near the line of divisions, which is 1\ inch from and parallel to the upper edge. 
The levelling screws enable me to bring the upper edge and therefore the line of 
divisions truly level, and this is finally tested by observation with the telescope and 
swinging mirror. The rods u and v are then gently worked in or out as needful 
until an observer with his eye at the window of the apparatus in the place of the 
mirror sees the window reflected from the clear glass on the line of divisions. The 
silvering of the middle of the scale is not absolutely necessary, but it enables one 
more quickly to recognize the position of objects placed against the lower part of the 
apparatus and so acts as a finder. When the scale is thus adjusted and has been 
placed with its divisions on a level with the mirror, a division not far from the middle 
will be the point at which a perpendicular dropped from the centre of the instrument 
will cut the scale. The eight pinching screws are then clamped and this division is 
recorded when its position has been more accurately determined by the use of a small 
telescope in the place of the eye. The division 2260 was the perpendicular reading 



NEWTONIAN CONSTANT OF GRAVITATION. 15 

in all the experiments made up to the present. The dummy was provided partly to 
absorb radiation from the flame and so to protect the working scale from heating, 
but mainly so that I should have a glass plate ready to divide myself without loss of 
time in case of accident to the working scale. This happily has not occurred. 

I calibrated this scale by reference to an American steel scale divided into 50ths 
of an inch, the uniformity 'of which I had previously tested. This steel scale became for 
the purpose of the angular measurements the standard to which everything was 
referred. For this purpose its absolute value is of no consequence ; all that matters 
is its uniformity. A long board was supported so that its upper surface was every- 
where level. Sheet lead strips were rolled until they were just thicker than the steel 
scale and a double row were laid upon the level board. The glass scale was made to 
rest upon these with its face downwards and the steel scale was slipped undenieath, 
so that the glass and steel divisions should be superposed. An erecting eyepiece was 
placed on a stand above the glass and was used as a reading microscope. Every tenth 
division was observed, and the 480 corrections were entered in a book, and were 
also plotted out on an enlarged scale, so that an error of j^q inch should be repre- 
sented by yq inch. From the irregular curve drawn through all the points the 
calibration error of every scale reading was afterwards ascertained. In order to 
determine the circular error, the true distance in scale divisions between the mirror 
and the scale was measured according to the plan to be described on p. 17. A large 
number of values of the circular correction were calculated from the expansion 
for tan -1 x and tabulated in terms of scale divisions. It was necessary to include 

as 5 
the term + — as at the ends of the scale this amounted to half a division, while at 
o 

1800 divisions on either side of the perpendicular reading it was one-tenth of a 

division. The perpendicular reading 22,600 being invariable, these corrections were 

plotted on the same sheet as the calibration errors, thus the two corrections could 

be taken out simultaneously for every reading which was thus converted into the 

reading that would have been obtained if every division subtended the same angle at 

the mirror. In this way the time and labour that are ordinarily required in finding 

the angles corresponding to scale divisions and in correcting for calibration are 

reduced to a few seconds for each, and error is almost impossible. 

Tlie Overhead Putties. 

The overhead wheels are eight in number, and are all of the same size. Five are 
over the instrument, and three close to the west wall. As already stated the edge 
of the middle one, which has a round groove in it, is exactly over the centre of the 
apparatus. Those on either side have flat-bottomed grooves, and they can be placed 
either 6 or 4 inches apart, according as 4^ or 2^-inch balls are to be used. Outside 
these, and the same distance apart as the screwed pillars K Pv in the lid, are two round 



16 PROFESSOR C. V. BOYS ON THE 

grooved wheels. The central wheel of the set near the west wall is round grooved, 
and the other two, which can be set either 6 or 4 inches apart, have flat-bottomed 
grooves. The purposes which these wheels serve are numerous and important. In 
the first place the middle ones are employed to reduce the frictiou of the lid, as has 
already been explained. In one of the cathetometer operations the lead balls and the 
tops of their supporting pieces have to be observed in order to find the levels of their 
centres when they are hanging out of sight inside the apparatus. At the same time 
the lid must be raised, and held out of the way ; but it cannot conveniently be 
removed altogether. To accomplish this, steel bands are passed over the flat-grooved 
pullies, and are each of them pinned to the ball holder at one end and hooked to an 
exactly equal counter- weight at the other. The balls can then be raised, and will 
remain hanging at any level at which they may be left. Two cords are hooked on to 
the eyes of the pillars II R of the lid, and after passing round the outennost pullies 
above, converge, and then, becoming single, pass over the central pulley next the 
west wall. There, a weight exactly equal to the lid, serves to counterbalance it. so 
that it will remain suspended in a horizontal position at any level. The height is so 
chosen that one of the ball holders is just above the pillar on its side, while the other 
is just below the lid on the other. The balls are then at the same level, and their 
upper portions can be seen just above the edge of the casting C. The balls under 
these conditions hang quite freely, neither touching the instrument nor being deflected 
by contact between their wires or steel bands with the lid. The steel is necessary to 
give definiteness to the positions of the lead balls during the cathetometer measures 
as if they were to hang from cord the twisting and uncertain and variable stretching 
would make accurate measurement impossible. The central overhead wheel alone is 
employed in placing the small balls in position. I used at first, after fixing them to 
their own fibres and hooks, and measuring the distances when hanging from the point 
of the hooks to the tops and bottoms of the balls, to get them in through the window, 
supporting the hook by a bent pin held in one hand and passing the fibi^e over a bent 
pin held in the other. The process was one of great delicacy and difficulty, but it 
answered with gold balls '2 inch in diameter. It was, however, next to impossible 
with balls of double the weight, as the fibre would not, under such a strain, bend 
round a pin, a polished steel rod, or anything that I could think of. I had therefore 
to adopt the plan with the overhead wheel, which has never failed. A pin, with the 
point bent at right angles to form a horizontal hook, is tied to a piece of sewing silk, 
and allowed to hang from the central pulley. A weight equal to the ball is tied to 
the other end. The pin-hook is inserted in the eye of one of the hooks and eyes 
from which the gold ball is suspended, and pulled up till the ball is over the tube. 
It is then let down until the eve is opposite the window, when its hook is made to 
rest upon the point of a large pin held in one hand ; by this means it is transferred 
to the side hook where it is left hanging by its eye, and ready to be placed upon the 
arm of the mirror when that is in position. 



NEWTONIAN CONSTANT OF GRAVITATION. 17 

The Steel Tape, and its Accessories. 

In order to make an accurate determination of the optical distance between the 
reflecting- surface of the mirror and the foot of the perpendicular upon the scale, I 
have prepared a steel tape to lie upon the beams L : and L 3 already described, and 
two sliders, one carrying an erecting eyepiece or low power microscope, and the other 
a sliding brass rod. 

The steel tape is one of ordinary construction, half an inch wide, and divided on 
one side in millims. and on the other in inches and eighths. As the lines on this, as 
is necessary with etched tapes, are thick and raised above the general surface, I 
engraved fine lines on the divisions— 2 inch ; 7 ft. 4 in. ; 14 ft. 6 in. ; 21 ft. 8 in. ; 
and 21 ft. 9 in. After removing the lead slips which had supported the glass scale 
while it was being calibrated, I laid this scale face downwards on the steel tape, 
setting of the glass scale upon the first engraved line at 2 inch. The reading in scale 
divisions of the fine line at 7 ft. 4 in. was then observed to be 430 2 - 5. The tape was 
drawn back until of the glass scale was over 7 ft. 4 in., and the reading taken for 
14 ft. 6 in. ; this was 4302-85. The readings for 21 ft. 8 in. and 21 ft. 9 in., taken 
in the same manner, were 4302"5 and 4352 - 5. The temperature was 19°'75 C. The 
calibration correction for the division 4302 of the glass scale is 3 - 0. Hence the 
distance in corrected scale divisions from the engraved lines at 2 inch and 21 ft. 8 in. 
at 19 0- 75 C. is 128 98 '85. The glass scale was calibrated in terms of the steel 
standard at 14° - 5 C. ; it had, therefore, relatively contracted at the higher tempera- 
ture. Taking "000002 as the differential coefficient of expansion, the distance 
between the engraved line becomes 12898'98 in terms of the divisions of the 
standard steel scale at any temperature. The sliders have bases made of plate glass, 
on each of which is an engraved cross line. One carries on two Y's the low power 
microscope, and this, after the tape is placed in position, is arranged with its cross* 
line over the engraved line on the 2 inch division. The microscope is then made to 
slide in its V's until a small cross engraved at the centre of the back of the freely 
suspended mirror is seen through the front window sharply in focus. The microscope 
is then clamped to its V's, and the slides moved out of position and again set several 
times, the relative position of the engraved lines being noted. If these are 'systemati- 
cally on one side, the microscope is shifted in its V's until repeated settings bring the 
engraved lines together. At the other end of the tape a corresponding slider is 
placed with its engraved cross-line over one of the engraved lines at 21 ft. 8 in. or 
21 ft. 9 in., and the brass rod is slid forward until it just touches the scale at the foot 
of the perpendicular from the mirror. The two sliders are then placed upon the 
original steel scale, from which the glass scale was calibrated, and moved until the 
fine lines on the end of the brass rod are seen sharply in focus. The distance between 
the engraved lines on the plate-glass bases, so determined, added to the distance 
between the engraved lines at 2 inch and 21 ft. 8 in. or 9 in., as the case may be, is 

MDCCCXCV. — A. D 



18 PROFESSOR C. V. BOYS ON THE 

the true optical distance from the reflecting surface of the mirror to the foot of the 
perpendicular upon the scale. This includes the small correction for the reduction in 
distance owing to the refractive power of the glass composing the mirror and front 
window. The divisions on the scale are, of course, placed on the side facing the 
instrument, so that no refractive correction is needed for the scale. 

The Optical Compass. 

In order to make the horizontal measures of the distances between the wires from 
which MM hang, and the quartz fibres which carry mm, measures which have to be 
made with the greatest possible accuracy, I had to design a special instrument which 
was suggested to me by Professor Clifton's optical compass. That is an arrangement 
by which two microscopes can be made to slide parallel to one another. After being 
simultaneously focussed on the two marks whose distance asunder is required, the 
frame to which they are clamped is rotated so as to bring them relatively unchanged 
in position to view a scale divided by lines microscopically fine. In this way the distance 
is directly transferred to a scale in terms of which it is known. In my case the chief 
difficulty was to keep the whole apparatus confined within the horizontal limit of 1^ 
inches, which was all I had liked to allow myself in the design of the apparatus itself. 
Into this space I had to get (l) a rotating slide to move on the lid round the axis of 
the apparatus ; (2) a focussing slide to move to and from the plane of the wires and 
fibres ; (3) a pair of traversing slides, each to carry one microscope capable of being 
separated by a fine adjustment and with a motion parallel to the planes of the fibres 
and wires. It was essential, moreover, that the slides should be very rigid, and that 
the focussing slide in its traverse should remain upon the same supports to avoid 
difference in flexure in case there should be any. The geometrical principle was of 
course followed, each moving piece resting on five independent small surfaces, and free 
from mechanical constraint. This instrument is shown in figs. 24 to 29. To avoid 
confusion, the rotating and focussing slides, with scale and micrometer screw only, are 
shown in figs. 24, 25, 26, in full lines upon the lid in chain lines, and the focussing and 
traversing slides in figs. 27, 28, 29. The rotating slide E, rests upon the lid by 
means of two curved V's, v x t\, resting in a circular V groove upon the lid, and by 
the flat surface f bridging the V groove at the back. It can, therefore, rotate upon 
the lid without shake, but no other motion is possible. This piece is made very stiff 
by the raised rib r round the triangular part, and by the overhanging ledge which 
extends over its whole width. The rotating slide also carries a micrometer screw S 
of 100 threads to the inch, with a head divided into 100 parts, and two parallelizing 
screws, S 2 S 2 . On the flat surface before S a S 3> a glass microscopically divided scale 
stands upon two little glass feet. Full particulars of this will be given after the 
description of the optical compass. It merely rests against the parallelizing screws 
and can be moved bodily to the right by the micrometer screw. No slide of any sort 



NEWTONIAN CONSTANT OF GRAVITATION. 19 

is provided, this simple construction, though perhaps less convenient, being far more 
perfect than any possible kind of slide. 

The focussing slide F rests upon R by means of the two V's, v 2 v 2 , which fit into 
a straight V groove in R, and by means of the flat surface f 2 , which rests upon 
a planed surface parallel to the v groove. This focussing slide is stiffened by 
longitudinal ribs above and below the general level, one on one edge, and the other on 
the other edge. It also carries a focussing screw S 8 of 50 threads to the inch 
roughly divided on the head. This merely pushes against the tail rib of R. causing the 
slide F to retreat from the centre of the apparatus. It can be moved the other way by 
hand, or by a gentle forward pressure on the screw head when it is being turned back- 
wards. As it is necessary to be able to give a fine focussing movement to this slide in two 
separate positions, about one inch apart, a focussing block b of the required length is 
pivotted on R, so that it may either remain out of use as shown in the figures, or may 
be brought under the focussing; screw after the focussing- slide has been withdrawn. 
A turn or two is all that is necessary then for the purpose of focussing in either 
position. 

Two traversing slides T l5 T 2 each rest upon the focussing slide by five small 
surfaces, of which four in each case are due to the long projecting V's v s on the front 
edge, of which the middle parts are scraped so as not to bear upon the longitudinal 

V groove in the traversing slide. 

The fifth point in each is formed by a small friction wheel w, which lies in a 
recess in the traversing slide, and runs upon a planed surface on T parallel to its 

V groove. The reason that I introduced a wheel here is, that while a very small 
vertical uncertainty is of no consequence, I was thus able to cause the whole of the 
fractional resistance to traversing to lie in the V itself, which is the more necessary as 
the distance between the ends of the V is necessarily less than the distance perpen- 
dicular to it. This is taken advantage of further, for I have arranged that the force 
that draws the two traversing slides together is produced by a long, very small helical 
spring of steel lying in a hole drilled in the V's themselves, thus being in the line of 
friction and producing no tendency in either to depart from its geometiical bearings. 
For the same reason I have made the fine adjusting screw which separates them act 
in the same line. This consists of a fine steel screw S 4 , fitting rather loosely in its 
very short nut, earned by T 2 at one end, and with a fine polished conical point at the 
other, which rests between a little V carried by T 2 and a vertical surface on T : . The 
screw and cone piece, therefore, are free from constraint, but simply push the 
traversing slides apart in the same line where the friction and the opposition of the 
spring act. Thus, when the screw is turned forwards, the slides simply separate to a 
minute extent, but have no tendency to lose their parallelism. Each traversing slide 
is furnished with three grooves cut away so as to support a microscope lying in any 
of them at each end only over small surfaces at 45° on either side, thus allowing it 
two movements, one of rotation, and one fore and aft. The latter is prevented by 

D 2 



20 PROFESSOR C. V. BOYS ON THE 

the use of focussing collars C, C, which slide stiffly on the microscopes and are so 
adjusted that when the two microscopes are alternately placed in the same groove 
and pushed up to their focussing collars they will each be in focus upon the same 
object. The positions of the grooves are such that the microscopes, when in their 
symmetrical positions, can be brought upon points distant from one another by 1, 4, 
or 6 inches, with a small margin on either side of a few hundredths allowed by the 
screw cone. Each microscope is furnished with a cross-wire and an eyepiece divided 
scale, one or other of which can be used according to the position of the positive eye- 
piece. If the microscopes are laid in grooves that do not correspond with one another, 
they may also be focussed upon points S&J-, 3^,. and 5 inches apart. If the two 
traversing slides are made to exchange places, for which purpose the screw cone has 
an extra nut and bearings provided, then distances of 2, 3, and i\ inches can be 
measured also, should any of them be required. 

Beyond stating now that the optical compass does a great deal more in the investi- 
gation than merely measure horizontal distances between vertical wires or fibres, and 
that the geometrical and rigid construction makes it possible to work to the full limit 
which optical definition imposes, I shall not at present explain the details and the 
order of the operations carried out by its aid. They will come more conveniently 
under the description of the experiment itself (Operation 9, p. 40). 

The Small Glass Scale. 

This was made for the optical compass by Zeiss. A strip of plate glass 6| X 1 X } 
inch was divided by lines microscopically fine as follows, A line was ruled at every 
inch from to 6, and at 2"50 and at 3'50 inches. In addition to these, five lines, 
Yoq of an inch apart, were ruled on either side of the divisions l - 00, 2 - 50, 
3'00, 3"50, 5'00, and 6'00. The five on either side of the zero were by inadvertence 
omitted, and the zero line was, by some obscure accident, ruled at "04 instead of at 
its true place. This, however, was of no consequence, as the 6 -inch distance was 
measured by reference to the divisions "01 and 6'03, 6"04, or 6'05. The 4-inch 
distance (not yet wanted, however), by reference to 1"00 and 5*00, and one or two 
contiguous divisions, and the small distance which was to have been 1 inch about, 
but which is in reality almost exactly - 9 inch by reference to 2'55 and 3"45. When 
I was in Cardiff at the meeting of the British Association, Professor Viriamtj Jones 
allowed me to measure the absolute distances between these divisions and a few on 
either side upon his measuring machine. This machine is one of Whitworth's ten- 
thousandth machines, but of more than usual stability, and with a bed long enough 
to take in bars three feet long. It is provided with a set of these bars increasing by 
inches from 1 to 12 inches, and with a 2-foot and a 3-foot bar. The glass scale was 
attached to the upper surface of the tail headstock by being simply pressed down 
edgeways upon two wafers of soft wax, and it was pressed endways against a third 



NEWTONIAN CONSTANT OF GRAVITATION. 21 

on the index. Safety fingers of wire were also attached to the headstock, but not in 
contact with the scale, so as to prevent it from falling, if it should by accident get 
displaced. One of the microscopes of the optical compass was allowed to rest in 
brass Y's bolted to a solid iron casting, which rested on the same slate-topped pier 
as the machine. The microscope was moved in its V's until one end of the scale was 
in focus ; the tail headstock was then traversed on the bed of the machine until the 
other end was opposite the microscope. The scale was then moved until this end was 
in focus, but the process, being only carried out by the fingers, was difficult to 
perform, as besides fixing the scale parallel to the bed as tested by the focus of the 
microscope, it was necessary also to see that it remained parallel in the vertical plane, 
and to adjust this by pressing out or adding to the soft wax wafers by which the 
scale was lightly held. At first this quadruple adjustment, in which the setting of 
one right generally put the other three out, seemed as if it would require for its 
successful accomplishment some mechanical contrivance more under control than the 
fingers. However, by a happy accident, I succeeded in soon getting the scale so that 
I could detect no want of parallelism either way with the fairly powerful microscope 
that I was using. The actual distances were determined along a line about -^ of an 
inch below the upper ends of the short divisions. 

The distances which it was necessary to know with the greatest accuracy, were 
those from to 6, from 1 to 5, and from 2\ to 3^. These were determined as follows. 
The loose headstock was traversed on the bed, and clamped when the division at one 
end of the distance to be measured was on the cross-wire of the microscope. A bar 
was then put in, the feeling piece put in its place, and the micrometer head turned 
until the feeling piece was just prevented from slipping, when the reading was taken. 
The headstock was undamped, moved, and the process repeated until two or three 
readings had been taken. The bar was then removed, the loose headstock moved 
until the division at the other end was on the cross-wire, and a new bar of suitable 
length put in, and the micrometer turned until the feeling piece was again just held. 
When the three readings had been taken in the second position, the headstock was 
set back to the first position, the first bar placed in position again, and three new 
readings taken ; then in the same way three more were taken in the second position. 
The microscope was not touched at all during the process. 

In connection with these measures, the following important details may be referred 
to I found great difficulty in setting the loose headstock by means of the high- 
p'.tched leading screw, especially as the wheel was almost out of reach, and in seeing 
the cross-wire in the eyepiece projected upon any division of the scale so as to bisect 
that division exactly. These difficulties were practically removed by placing the 
microscope so that its cross-wire was slightly inclined to the vertical in which 
direction the divisions are ruled, and by setting the ruled lines symmetrically between 
a pair of microscopically fine specks of dust upon the cross-wire which, with the 
particular inclination then, just lay on either edge of the line. The width of the line 



22 



PROFESSOR C V. BOYS ON THE 



itself was found to be 5^-0 inch. In this way there was no doubt as to the setting 
of the cross-wire accurately to a tenth of the thickness of the line. I was not, 
however, always able, owing to the circumstances to which I have already referred, to 
leave the headstock set and clamped so accurately in position, that I could detect no 
want of symmetry in the microscope. In a few cases I left it with a -f or — • error 
of one-tenth of a division as estimated by the eye, which error I entered in the note- 
book at the time, and before I knew what the reading of the Whitworth machine 
would be. These were taken by Mr. Harrison, the very skilful assistant in the 
Physical Laboratory at Cardiff, and he did not know what correction I had entered, 
or indeed, if I had entered any correction. His reading was then entered into the 
book also. In this way I hoped to avoid that spurious appearance of accuracy that 
is apt to result from knowing during a process of adjustment when the last setting 
has been reproduced. The temperature, of course, was frequently taken, but it only 
rose half a degree during the day, and to avoid as far as possible differences in 
temperature in the apparatus, the bars that were used were kept during the measure- 
ments upon the bed of the machine. As an example, I give the figures of the middle 
inch exactly as they were entered. The whole numbers represent yoo ptlis, and the 



decimals 



100000 



ths of an inch. 



Division on 
Scale. 


Bar used. 


Reading and 
correction. 


Reading and 
correction. 


Reading and 
correction. 


2* 
3| 

2i 

3^ 


9-inch 

8-inch 
9-inch 

8-inch 


f 315-1 

I ~-2 
313-3 

3144 

/ 312-9 

I --2 


314-9 

313-4 

314-4 

312-8 


315-0 

313-4 

314-6 

/ 312-3 

\ +-2 



Temperature 16° - 9 C. 



The distance between 2\ and 3j on the scale found by taking the simple mean of 
the above figures and subtracting, is '99983 inch, or allowing for the gradual change, 
due probably to temperature variation, which seems to have been going on at this part 
of the day (about 1 p.m.) more particularly, the distance is "99986. 

A determination, made early in the afternoon, of the same distance by direct com- 
parison with the 1-inch bar, the 8-inch bar remaining in the machine, gave as the 
length of the middle inch of the scale '99979. Since the bars are not guaranteed to 
be nearer to the truth than 10 Q 00 th of an inch, the agreement between the 1-inch 
bar and the difference between the 8- and the 9 -inch bars is better than might have 
been expected. Meanwhile, I may consider for the present that the true length of 
the middle inch is known with an accuracy of 1 in 10,000 at least. I have taken it 
to be equal to '99980. 



NEWTONIAN CONSTANT OF GRAVITATION. 



23 



The interval 1"00 to 5 "00 was compared with the difference between an 11-inch and 
a 7-inch Whitworth standard bai\ Assuming the difference to be 4 inches, this 
interval was found to be 3'99970 inches. In the same manner the interval between 
zero (really 0"4) and 6 "00 was found by comparison with the difference between a 
12-inch and 6-inch Whitworth standard bar to be 5"95996 inches. 

The distance from 6 "00 to each of the divisions up to. 6 "05 was measured in the 
Whitworth machine, and also by means of the micrometer screw of the optical 
compass. The value of the screw was found in terms of the middle inch of the scale, 
which had been measured most cai'efully upon the Whitworth machine. The screw 
measures were found short by '145 per cent. Allowing for this the distances were 
found to be : — 









Corresponding totals 


Between 


By screw corrected. 


Total from 6-00. 


measured in 
Whitworth machine. 


600 and 601 


•010145 


•010145 


•01015 


6-01 ., 6-02 


•010105 


•020250 


•02019 


6-02 „ 6-03 


•009815 


•030065 


■03002 


6-03 „ 6-04 


•009915 


•039980 


•03995 


6-04 „ 6-05 


•010095 


•050075 


•05012 



Adding the measures of the intervals "04 to 6"00, and 6*00 to 6"04, the sum is 
5"99994 or 5 - 99991 according to the value taken for the smaller interval. Mr. Chaney 
allowed me to measure the distance from "04 to 6 "04, at the Standards Office, by com- 
parison with the intervals 24 to 30 and 30 to 36 in the standard yard measure. The 
two measures did not differ by an amount that could be detected and the result was 
found to be 5 - 99995 at the temperature 59°"7 F. There was no question, therefore, 
that the 6-inch distance was known correctly to one part in 100,000. 

The distances from 2*50 to 2"55 and from 3"45 to 3"50 were measured by the micro- 
meter screw of the optical compass, and their sum was found to be (employing the 
corrected value of the screw) "100125, so that the distance between the divisions 2 - 55 
and 3'45, which are those actually used in all the measures of the horizontal distances 
between the fibres, is "89967. There can be little doubt that this is correct to one part 
in 10,000 and, as a small error in the working length of the beam produces an error of 
about the same magnitude in the result, the value of G is not likely to be affected 
seriously by uncertainty in the value of this inch. I did not attempt to determine 
this inch at the Standards Office, as I found that, owing to the coarseness of the lines 
on the standard bars and the imperfect optical means, so small a distance could not be 
measured with a high degree of proportionate accuracy. Should the rest of the ex- 
periment ever be carried out with such perfection that a possible doubt of one in 1 0,000 
on this measure becomes of importance (and I see no reason why it should not), then 
I should have to rely upon a measurement made at the International Bureau at 



24 PROFESSOR C. V. BOYS ON THE 

Sevres, but up to the present 1 am quite content with that made upon the Whitworth 
machine. 

The Clock. 

The clock, the position of which is indicated in fig. 18, is a Frodsham regulator, 
which was lent to me by the late Professor Pritchard, who took a great interest in 
the experiment. The present owner has kindly allowed me to retain it until the 
work is finished. The clock is placed so that it can be seen from the observing stool 
at the telescope, and is illuminated when necessary by a small incandescent lamp. 
It is employed to mark time upon a smoked drum, upon which also are marks made 
by the action of a key at the telescope. I finally determined to employ the chrono- 
graphic method after seeing Professor Cornu's apparatus. To the lower end of the 
pendulum I screwed a platinum wire flattened and filed to a rounded edge at its 
end, the edge being in the plane of oscillation. This passes through a horizontal 
line of mercury, standing up by its capillarity above a transverse groove in a piece of 
wood. The end of the groove opens into a large well filled with mercury, so as to 
retain the purity and the level. The wood on either side of the groove is cut away 
to an edge, so that mercury dust carried over by the platinum cannot accumulate 
and give trouble. The wood is so placed that when the pendulum is moving through 
a small swing of a quarter of an inch only, the time marker actuated by the contact 
ticks regularly. With the full excursion the alternate marked seconds are then 
indistinguishable in length. I soldered two platinum wires to the second hand and 
brought an insulated elastic platinum point over the seconds dial and under the 
minute hand, so that the second hand should make contact twice a minute. I so 
bent the wires that at the minute contact should be made again immediately after 
the pendulum had broken contact, and retained till the end of the first second, while 
at the half-minute it was made again after the thirtieth second and immediately 
broken. The minutes and the half-minutes were in this way clearly and differently 
marked (fig. C, p. 48), and it was thus unnecessary to count more than 15 seconds on 
the charts. The time markers and the drum to cany the smoked paper were made 
by the Cambridge Scientific Instrument Company, and are of their well-known 
pattern. I took out the long heavy wires of the time markers, which, I understand, 
are made to the order of the physiologists, and replaced them by very small and 
light styles of copper foil tapering to a point. The two are arranged close together 
so that the tracing points are not more than yoo oi " an mcn a P ai 't- The sheets of 
paper, 12 X 19 inches, are most readily smoked when stretched on the drum by 
pouring a little benzine into the india-rubber pipe which supplies a fishtail burner. 
The very smoky gas flame which results rapidly produces a deep and uniform coat of 
soot. The sheets when finished are passed through a bath of very dilute shellac varnish, 
the strength being such that the smoke does not rub off, but may have numbers, &c, 
readily scratched upon it with a pointed style. The drum is driven through worm 



NEWTONIAN CONSTANT OP GRAVITATION. 25 

gearing by a P 1 electric motor, by Cuttriss, of Leeds, the current being supplied by 
a couple of E.P.S. cells. Mr. F. J. Smith has kindly allowed me to charge them 
■when required at his laboratory. The same cells are connected up to the two 
time-marking circuits, and to a small electric lamp placed in the octagon house 
to illuminate the vernier and divisions close by. This is lighted by raising, and so 
making the upper contact of the key, which on depression is employed to make the 
signal marks from the telescope. Owing to the self-indication of the small electro- 
magnet of the time marker, a considerable spark would be formed at the mercury 
break in the clock, to the destruction of the contact, if it were not for two electrolytic 
cells in series, charged with battery acid and with platinum electrodes, which are 
employed as a bridge across the clock break. This sets up an electromotive force of 
polarization which prevents any current from passing when the contact is kept 
broken, but its resistance is so small that the high electromotive force set up at the 
break is able readily to fall through them, thus practically abolishing the spark. 
I found this greatly superior in every way to a non-inductive resistance. There 
is one point connected with this break which I believe to be worth recording. To 
ensure good contact I. amalgamated the platinum point with sodium amalgam, but 
immediately found that the contact lasted longer, and was more irregular than 
before. However, I left the point amalgamated for a fortnight, during which it gave 
more trouble by drawing the mercury out of the trough. I then unamalgamated it 
by holding it over a candle flame, until I concluded that the mercury was all gone. 
I did not make it very hot. Since that time the contact has never failed, which it 
occasionally used to do before. I attribute the improvement to an atomic roughening 
produced by the penetration of the mercury. Before the point was unamalgamated, 
the pendulum, as I afterwards discovered, made a second contact with a pool of 
mercury drawn out of the trough and electrically insulated, which contact mechani- 
cally disturbed its period. For this reason Experiment 4 is incomplete, as its time 
observations are untrustworthy. I took, however, the rigidity of the fibre from 
Experiment 5, and so completed the calculation. 

The Large Balls and their Supports. 

One of the difficulties in the preparation of apparatus for measuring the mutual 
gravitation of comparatively small bodies is met with in making the large balls. 
Cavendish employed large balls of cast lead 1 foot in diameter. Professor Poynting 
made the balls in his apparatus of an alloy of lead and antimony, for the sake of the 
extra hardness, which would make it easier to turn them accurately to form and would 
render them less liable to subsequent deformation. Though special precautions were 
taken to avoid cavities, and to obtain homogeneity, the large one was found to 
act differently in different directions, and he localized a cavity by observations 
in this way. Afterwards he found the centre of gravity was to one side of the 

MDCCCXCV. — A. E 



26 PROFESSOR C. V. BOYS ON THE 

centre by an amount corresponding very nearly with that which he had deduced 
from his gravitational observations. I do not feel satisfied myself that this affords any 
proof of the existence of an actual cavity, as a gradual variation of density, such as might 
easily occur in an alloy, might have produced the same effect in each case. For this 
reason, when a much higher degree of accuracy is being sought for, I consider that alloys 
are fatal to success. Professor Coenu has without any doubt avoided any uncertainty 
as to cavities or uniformity of density, or probably truth of form, by employing 
mercury aspirated from one pair of spherical hollow cast-iron moulds to another pair 
so placed as to reverse the attraction. By this means it seems to me everything may be 
known with more than abundant accuracy, except the actual position of the centres of 
the spheres, or what comes to the same thing, their actual distances from the centres 
of the attracted masses. As I explained in my first paper, in my arrangement, the 
difficult geometrical measurements are almost all made of secondary importance. A 
small uncertainty in the levels is, as in previous arrangements, of secondary importance, 
as in this sense they are at a position of maximum effect. A small uncertainty of the 
angle of azimuth does not matter, for this also is at a position of maximum effect. 
If there is a small eccentricity of position of the gold with respect to the lead balls, 
either in the plane of the lead balls, or across that plane, again the effect is infini- 
tesimal, for the departure is from a minimum of effect in the first case, and a maximum 
in the second. The only measures of serious importance, on the accuracy of which 
the result directly depends, is the distance in plan from the centre of one lead ball to 
the centre of the other, and the corresponding distance in the case of the gold balls. 
In the first there must not be an uncertainty of ^-oVo °f an inch, or in the second 
°f ro;o~oo 0I " an inch. I do not think it would be possible on Professor Coenu's plan 
to obtain a knowledge of the positions of the centres of the mercury spheres, especially 
when one is six inches above the other, with anything like this degree of accuracy, 
and therefore, though with the large apparatus he used, and the proportionally 
lower degree of accuracy that was sufficient, the plan is most excellent, and answers 
perfectly, it would not be suitable in the present case. Thei'e is a second objection 
depending upon the magnetic quality of the iron moulds. For though to ordinary 
tests the beam and gold balls are not affected by magnetism, I have felt that in 
measurements of forces of such supreme delicacy it is safest to avoid introducing 
magnetic materials, lest any systematic disturbance should be introduced. I have 
however, satisfied myself by experiment since putting up the apparatus, that a 
magnetic force much greater than that due to the earth produces no effect. 

The plan that I have adopted seems to me to be free from the objections that I 
have urged, to be easily carried out, and to be specially adapted to the purpose of 
exact measurement of the distance in plan from the centre of one ball to the centre of 
the other. 

Mr. Monro, who has special experience in accurate spherical work, made the cast- 
iron mould shown in figs. 16 and 17. The internal hemispheres are turned out so 



NEWTONIAN CONSTANT OF GRAVITATION. 27 

truly that the steel disc used as a template would audibly rattle when placed in 
either alone, but could not be got in at all when a single strip of cigarette paper was 
inserted on one side only. The two halves can be screwed together by means of six 
steel bolts as shown. A ^-inch hole is bored in the centre of one hemisphere and 
one of f-inch in the centre of the other. Into the latter an accurately fitting steel 
plunger was inserted, and when pressed down to the head, was turned at the inner 
end, so as to complete the sphere. A small hole is drilled on the equator, enlarged 
almost immediately to a greater size. Into this a brass plug can be pushed. Before 
being used, the mould is warmed, and the internal surface smoked with a gas flame. 
Into the ^-inch hole the brass ball-holder e is inserted. A number of these were made 
by Mr. Colebrook, of the utmost possible accuracy of the form shown, this being a 
■|-inch sphere, surmounted by a £ X 5-inch cylinder with a shoulder of -g% inch, of 
such a depth that when pressed home the -|-inch sphere should be tangential to the 
4^-inch sphere. Though these ball-holders were made to measure only, their weights 
were closely alike, being 10 "70 grams for each before cutting the slot and drilling the 
cross hole, and 10 '2 8 afterwards. Since the whole effect of the gravitation of these 
ball-holders and of the 4^-inch lead balls, all in their ultimate positions, is 7-3V0 in- 
excess of what it would be on the supposition that the whole mass is concentrated at 
the centres of the lead balls, any doubt as to the amount of the correction, which 
cannot be so much as one part in a hundred, leaves an uncertainty in the result of 
about one part in a million, and is of no consequence. I should state here that this 
correction includes the very small pieces of brass fastened to the lower end of the 
wires, which with their pins were made to occupy the same volume as the material 
removed in the slot and cross hole. The brass ball-holder, before being inserted 
in the smoked mould, was tinned on the spherical surface, and then wiped to remove 
superfluous metal. The mould was then put together, and the steel bolts, after being 
well rubbed with blacklead, screwed up as tightly as possible. The mould was then 
slowly heated over a Fletcher gas burner, until a piece of lead lying upon it began to 
melt. The brass plug was then inserted in the side hole, and pure skimmed lead 
was gently poured in through the neck from an earthen pot until it was full. The 
mould was then lifted on to a cold block of iron, but a large blow-pipe was kept 
playing on the top of it, the effect of which was that the metal slowly solidified from 
below upwards. The progress could be followed by inserting a fine carbon rod, or 
more evidently by watching the contraction of the metal in the neck. It was 
necessary to add lead from time to time to keep the neck full, and in the case of the 
4j-inch ball the amount required would have filled about 3 inches of the neck had 
it been so long. In this way perfectly sound castings, free from vacuous cavities, 
which always form when the metal solidifies on the surface first, are easily obtained ; 
but to make the metal free from pores, and to close up any such cavities should they 
by any possibility exist, the moulds were placed in the hydraulic press immediately 
the metal in the neck had become solid, and after removing the brass plug, the steel 

E 2 



28 PROFESSOR C. V. BOYS ON THE 

plunger was forced down upon its shoulder. The solid metal was thus under great 
pressure made to flow, and a quantity of wire was forced out of the small side hole. 
Under these circumstances cavities are impossible, and since pure metal was employed, 
variations of density were out of the question. It may be worth mentioning here 
that of all metals in commerce, lead may be obtained of a greater degree of purity 
than any other. As soon as the pressing had been completed, the mould was 
removed, and allowed to cool. On being opened the lead ball was found perfect in 
form, and, so far as it is possible to judge, perfect in every respect, or at any rate so 
perfect that any departure from such a state cannot produce a disturbance in its 
gravitative power which is comparable with the limits of accuracy with which the 
attractions can be observed. I have made four balls of the 4|-inch size, numbered 1, 
2, 3, and 4, but I have at present used only numbers 1 and 2. Besides these I have 
made four of the smaller size of 2\ inches in a mould of the same construction and 
numbered them numbers 6, 7, 8, and 9. To avoid risk of injury, the balls are kept 
in pairs in four well-made mahogany boxes, with two velvet-lined hemispherical 
hollows, in each half of each of the boxes. I have made lifters also to raise them by 
their brass lugs. 

I weighed these balls on August 18, 1891, on the large Oertling balance in the 
South Kensington Museum. Through the kindness of Mr. Chaney I was able to 
find the true value of all the weights employed, by comparison with the standards 
at the Standards Office. The weights of the two lead balls made use of, with their 
included brass ball-holders are, taking due account of the corrections : — 

No. 1 7407-47 grams. 

„ 2 7408-13 „ 

The lead balls are suspended from the geometrical clamps at the tops of the lid 
pillars by jmosphor-bronze wires, which I drew myself down to the smallest size that 
I considered safe. This was found by measure to be "0232 inch in diameter. As it 
had to carry 16'33 lbs., the stress would be one of between 15 and 16 tons to the 
square inch only, or about one-third of what I had found the wire able to carry. I 
could not silver-solder the wire into the upper and lower connecting pieces, as the 
strength was destroyed by annealing, and I found that soft solder allowed it slowly 
to creep out even when it was soldered into a hole which it nicely fitted, and j inch 
long. I overcame this minor difficulty by dipping the ends of the wires into copper 
solution and thickening them by electro-depositing copper until they were just too 
large to enter the enlarged holes prepared for them. I then drew them through holes 
in a draw plate down to the right size. They were then sweated into their places, 
and the end of the wire at the upper end bent over at the bottom of the slot where it 
just protruded, hammered down and again sweated ; while at the lower end a small 
transverse hole was drilled on each side so as just to touch the side of the wire, and 
pins driven in, and the whole sweated together. This was done on September 2nd, 



NEWTONIAN CONSTANT OF GRAVITATION. 29 

1892, and though the wires have carried the balls ever since, they have not broken, 
stretched, or drawn out. The wire, as it left the draw plate, was free from kinks, 
and was not allowed to be bent afterwards. As it is stretched so severely, I have 
assumed that the centre of gravity of the suspended ball is vertically below the axis 
of the wire, measured at a point nearly 2 inches below its point of support. The 
actual horizontal distance between the axes of the wires at this level can be deter- 
mined with the optical compass, with an accuracy of 10 1 000 inch ; and therefore I 
maintain that this, the most important of the geometrical determinations, is known 
with abundant accuracy. 

Tlxe Small Balls or Cylinders. 

Owing to the small size of the attracted masses, I was able to make them of pure 
gold, a metal which possesses all the advantages of lead, besides increased density 
and freedom from oxidation or corrosion. As the inside of the central tube of copper 
in which the gold balls move is polished and electro-gilt, and as they move about an 
axis which coincides with the axis of this tube, any attractions or disturbances due to 
difference of electrical potential after contact must be of the smallest order possible. 
The method of making the gold balls is somewhat similar to that followed in the case 
of the lead balls, the difference in procedure depending upon the nature of the metal 
and the reduced size. Mr. Colebrook made for me pairs of hardened steel bars, with 
ends ground out and polished to true spherical surfaces, each of them just under a 
hemisphere in extent of surface. These were made in pairs for spheres of diameter, 
"2, "25, and "3 inch. The quantity of gold necessary for making a ball, plus a small 
excess for waste, was placed in a hollow in a piece of Bath brick or of prepared char- 
coal, and heated with an oxy-hydrogen jet with just enough oxygen to melt the gold 
until it had run down to a clean button. When this was allowed to cool by itself, 
the surface was drawn in by the contracting centre, and a cavity and dimple were 
formed. When, however, the flame was gradually withdrawn, or reduced in size, so 
that the metal solidified from below upwards, a solid button with a perfectly smooth 
surface was easily obtainable. The button so formed was placed in one of the hemi- 
spherical moulds, held in a vice, and covered with the other, which was then given a 
smart blow with a hammer. The gold was thus compressed to an almost spherical 
form with an equatorial rib. On being turned over through a right angle, the rib 
was compressed into the gold, leaving a projecting head on each side, and these were 
finally compressed into the gold after a further twist through a right angle. The 
gold was then annealed, and beaten in the moulds with gradually reduced blows, 
being turned between each blow. When the ball was made practically perfect, it was 
weighed, and brought down by a very fine file to within 1 milligram, of the ultimate 
weight. It was then annealed and gently beaten again with rapid light blows, being 
turned between each, until a highly polished perfect sphere was the result. Rubbing 
with wash-leather and a little rouge brought it to the required weight, when it was 



30 PROFESSOR C. V. BOYS ON THE 

finally gently beaten in the mould. These balls were made in pairs, identical in 
weight, so far as I could determine with the balance. The smallest weighed 
1"29S3 grams each. The point of a fine needle, held in a special tool in which the 
ball was placed, was forced a short way into the gold, and removed, after which the 
ball was replaced in the dies and compressed again, which process foi*ced down the 
very small elevation round the little hole, and left a much smaller hole than could be 
made direct. In order to fasten these balls to their respective fibres, a pin was 
dipped in shellac varnish and rapidly passed across the end of the fibre. After one 
or two trials, a semi-microscopic bead of varnish, formed by capillarity, was left just 
above the end of the fibre. This was then placed in the little hole in the ball, and 
the latter was placed in a conical hole in a brass blank, which had been warmed in 
the flame of a spirit lamp. Under the influence of the warmth the little bead slid 
down, and instantly flashed into vapour as it touched the gold ball. If necessary, a 
small quantity more varnish could be applied upon the point of a very fine needle. 
The ball thus attached formed the lower part of a perfect Borda pendulum, there 
being nothing visible outside the spherical surface. So perfect is this mode of support 
that when a gold ball is hung up by its fibre, and set in torsional vibration, the image 
of the window seen reflected on the spherical surface was not seen to move or quiver 
when examined by a strong lens. The upper end of the fibre was fastened with 
shellac to the tail of the hook and eye, seen in fig. 7, the length of course being 
adjusted so that the gold and lead ball would hang at the same level. 

There is no question that this is the most perfect method of holding the gold balls, 
but when I came to the larger size of '25 inch, weighing 2 - 6501 grams, the risk 
of fracture due to an accidental roll of the ball was increased, and in one case, after 
a week spent in making all the preliminary measurements, one of the balls drew off, 
owing to imperfectly dried varnish, and it and its companion and the mirror were all 
precipitated down the central tube and the torsion fibre was lost. To reduce the 
risk, I therefore arranged another process which is practically as good and is much 
safer. A piece of No. 40 copper wire, -§ inch long, weighing "00084 gram, was 
inserted into the hole, and soldered in its place with a scarcely visible amount of 
solder, the wire and solder weighing exactly "001 gram. A calculation of the total 
attraction of ball and wire, on the supposition that the wire as well as the ball acts 
upon the centre of the lead ball as if it were concentrated at the centre of the gold 
ball, shows the error to be only 2 5 J g of the whole, it is therefore of no consequence. 
To the side of this wire the quartz fibre was easily fastened with shellac varnish, the 
amount of shellac used being - 0001 gram, or even less. I have not made any balls 
of the largest size, but in the one experiment in which larger masses were employed, 
have made instead cylinders of gold, ^ inch in diameter and "2587 inch long. These 
were prepared in a similar manner. Mr. Colebrook made for me a hardened steel 
cylindrical mould, the inside being lapped out to size and polished. The end was 
made plane and truly perpendicular to the cylindrical hollow. A polished steel plane 



NEWTONIAN CONSTANT OF GRAVITATION. 31 

was kept pressed against this face by screw pressure, and a steel plunger, accurately 
fitting the mould, with a polished plane perpendicular end completed the tool. The 
required quantity of gold, plus a small quantity for excess, was melted into a button 
as before, and placed into the mould. The plunger was beaten with a heavy hammer, 
under the blows of which the solid gold flowed as freely as the lead in the other case, 
penetrating the fissure between the cylinder and the bottom slab. A second plunger, 
made of brass, with an exactly central, fine needle point, was then pressed with light 
blows upon the gold to make a central hole, into which to solder a supporting wire, 
as in the case of the gold balls. Mr. Edser, of the Royal College of Science, was 
kind enough to calculate for me, by means of spherical harmonics, the very small 
difference between the attraction of the cylinder upon a point at the centre of the 
lead ball, and that which would be exerted if the whole of the mass of the cylinder 
were concentrated at its centre. The correction is for a greater variation of distance 
and of inclination from the equatorial plane than can have been met with — "00030 
of the whole, and this correction is accordingly applied in the one experiment (9) in 
which the cylinders were employed. 

I have not at present referred to the attractions between the suspending wires and 
the gold balls, and between the suspending quartz fibres and the lead balls. The 
attractions of the fibres and wires for one another are, of course, infinitesimal to the 
second degree. Calculation shows that in experiments 4 to 8 and 10 to 12, the 
attraction of the lead balls for the fibres is to their attraction for the gold balls as 
1 is to 204,500, and in the same direction, while the attraction of the gold balls 
for the wires is to their attraction for the lead balls as 1 is to 115.000, and in the 
opposite direction. The reversal of the direction is surprising, but it is due to the 
fact that the most effective part of the fibres is absent in the case of the wires, owing 
to the large diameter of the lead balls, and, therefore, the action of the long wire on 
the upper gold ball, which is on the other side, is the preponderating influence. The 
difference of these two corrections is -^-gT&oTf 0I " the mam effect, and in the opposite 
direction. I should add, that though the absolute masses of the small balls are known 
with an accuracy of 1 in 10,000, this is in no way necessary, So long as they are 
practically alike, it does not matter whether their mass is known or not, as it is 
ultimately eliminated. I have, however, introduced into the numerical work the 
actual masses in order to obtain the constants of the fibres and of the mirror, and the 
viscosity of the air absol utely. 

The Beam Mirror and its Attachments. 

One of the most important parts of the whole apparatus, and certainly the most 
difficult to arrive at in perfection, is the combination of beam and mirror which shall 
support the gold balls definitely in position, and shall, in its capacity as mirror, make 
it possible to determine their position with the greatest possible accuracy. In my 



32 PROFESSOR C. V. BOYS ON THE 

paper on the radio-micrometer," I dwelt on the importance of the proper propor- 
tioning of the mirror to the rest of the suspended body. Then I only considered its 
moment of inertia and weight. In the present case these remain important, and 
there is besides the resistance to motion due to the viscosity of the air, which unfor- 
tunately is of the most serious moment. If the usual round mirror is employed, the 
definition, as is well known, is directly proportional to its diameter — that is, if its 
figure is perfect. The advantage of a large mirror is somewhat counterbalanced by 
its weight, which tends to break the fibre, so that lighter balls or a coarser fibre are 
necessary ; by its moment of inertia, which increases the already prolonged period ; 
and by the resistance which it meets with in moving through a viscous atmosphere. 
As it is important to keep the mirror or mirror and balls swinging as long as j)ossible, 
in order to determine their periods accurately, a high decrement is most objectionable. 
By making the mirror in the form of a long bar, I have succeeded in partly reconciling 
the incompatible conditions, for not only may the weight and moment of inertia be 
reduced to less than half of that which would be due to a disc of the same diameter, 
but the definition is decidedly better, as I have proved by experiment, and as is 
shown by optical theory. I should have said that the definition in a direction 
parallel to the length of the bar is better, that at right angles being obviously not so 
good. For the purpose of reading the divisions of a horizontal scale, vertical definition 
is of consequence only in so far as it is sufficient for the purpose of reading the figures 
attached. These I had made large with this object. I have already stated that the 
scale is formed by black lines on a luminous ground. By this means I am able to 
obtain a degree of reading power which might seem beyond that which a mirror of the 
size used ought to give. The mirror will form a spurious image of a luminous point 
of an oblong form, the long dimensions being vertical, and bearing the same relation 
to the shoi't as the length of the mirror, which is horizontal, bears to its breadth, 
which is vertical. If the mirror could be made indefinitely long, the image would shrink 
to a vertical line, and horizontal definition would be perfect. Owing to the limited 
length of the mirror ( - 9 inch, about) the width of the spurious image subtends an 
angle of about 5", and this is the limiting separating power in the horizontal direction. 
Now, if the scale were made by very fine wdrite or luminous lines upon a dark ground, 
each line would be seen as a band with shaded edges 5" wide ; but, as the angular 
distance which I have been able to employ from one division to the next is only 14", 
the lines would have appeared half os broad as the spaces. If the lines on the real 
scale were of sensible thickness, then the proportion of apjaarent line to space would 
have been higher. If, on the other hand, the ground is luminous, the lines are dark 
and are made rather coarse ; the effect of the spreading of the light is to pare off the 
dark edges, and leave the appearance of a finer line, which, though it is not sharp, is 
symmetrical, and, as a recurring phenomenon, allows of definite observation to one- 
tenth of a division, i.e.. in the actual case to 1'4". This corresponds to a movement 

* ' PLil. Trans.,' Jan., 1S89. 



NEWTONIAN CONSTANT OF GRAVITATION. 33 

of the mirror of - 7", and of the balls of 7To7o"o"o inch. To this degree of accuracy 
there is no difficulty in observing- ; in fact, I might have made the divisions smaller, 
and still have been able to read to tenths. Of course this perfection is only possible 
with a very perfect mirror, and for this I applied to Mr. Hilger, who took special 
pains in preparing several as thin as he dare. Of these, one only, when tested while 
still round with the large astronomical telescope upon an artificial star, was perfect 
in its definition, and formed the spurious disc and diffraction rings equally in all 
directions. This mirror was the one employed in all the experiments up to date. A 
second one was nearly as good. One made of quartz showed the diffraction rings 
strongly in three directions only, 120° apart. In making the test I was careful to 
notice in which direction the two images, one due to the front surface and the other 
to the silvered back surface, were separated, owing to the inevitable want of perfect 
parallelism between the faces. I then cut them in such a direction that the displace- 
ment should be vertical, so as to avoid the confusion caused by the superposition of 
the dim reflection of the scale upon the image under observation. The two good 
mirrors I slit with a fine steel disc and diamond dust, so as to leave a central bar 
\ inch wide. This gives abundant light, and defines well enough to enable the 
figures to be read. I found by the use of screens that a bar ^ inch wide, though it gave 
enough light, so destroyed the vertical definition that the figures could not be read, 
and the long and short lines were not so clearly distinguished. I then, with a very 
shai'p-edged brass disc and washed emery, ground in the thickness of each mirror at 
each end a vertical V, seen in the plan (fig. 7). The bottom was so fine and sharp 
that a quartz fibre ToVo i ncn m diameter would rest definitely in its place. The 
mirror was cemented with three spots of shellac varnish to the gilt copper support 0. 
This was so formed that the balls could hang by their eye-hooks from the notches at the 
end of the arms, with the fibres resting in the vertical V orooves of the mirror. The 
beam mirror was carried by a quartz fibre, fastened to the point of by shellac in all 
experiments up to No. 3, and soldered to an intermediate tag in the later ones. The 
details of the soldering process are given in the ' Phil. Mag.' for May, 1894. From the 
lower central hook of the beam mirror the silver counterweight K may be suspended 
when the gold balls are removed. This was turned by Mr. Colebrook out of pure 
silver, which I had prepared by casting and hammering. It is truly cylindrical, and, 
with the triangular wire hook to which it is soldered, weighs exactly the same as the 
corresponding pair of balls with their fibres and hooks. Its diameter was measured 
in several places with a screw micrometer. The weight of the cylinder, of the little 
hook, and of the solder used were separately determined, and the very small radius of 
gyration of the hook estimated from its dimensions and form. The period of the mirror 
was observed (a) with the balls on, (b) with the counterweight on, and (c) alone. From 
(a) and (b) the unknown moment of inertia of the beam could be determined, and 
from a, b, and c the effect of the stretching upon the rigidity of the fibre could be 
ascertained. The suppositions made are rather numerous, and are best discussed here, 
JIDCCCXCV. —a, E 



34 PROFESSOR C. V. BOYS ON THE 

In the first place it is supposed that the mirror does not change its axis when 
swung alone or with the balls or counterweight suspended, for, if it does, its unknown 
moment of inertia will not be a constant, as assumed. Secondly it is supposed that 
when the gold balls are suspended from the beam mirror, they are ligidly connected 
with it, or that the mobility of suspension or torsion is so minute as to be equivalent 
to a rigid suspension. Thirdly, that the counterweight, when suspended from the 
beam mirror, is rigidly connected with it, and that it rotates about its geometrical 
axis. It is obvious that however carefully the parts have been made, the suppositions 
cannot be rigidly true. It is necessary, therefore, to find what order of error is intro- 
duced by any possible or observed want of perfection. 

It is evident that the axis of rotation of the mirror must always pass through the 
point at which the quartz fibre leaves it, and that, when it is unloaded, its axis passes 
through its centre of gravity. As the construction is intended to be symmetrical 
with respect to this axis, and is so, as far as observation enables one to judge, and as 
such an axis is an axis of maximum or minimum moment of inertia, the uncertainty 
in the moment of inertia, due to a small angular displacement, is proportional to the 
square of the angle, and is altogether beyond the region of experimental certainty. 
When, however, the balls or counterweight are placed in position, if the construction 
is not truly symmetrica], the beam mirror Avill now rotate about an axis which does 
not pass through its centre of gravity. In an experiment made for the purpose, this 
displacement, when the larger balls were suspended, was found to be , 0063 inch, an 
amount considerably larger than I had expected. In this case the moment of 
inertia, added to the whole combination on this account, is, weight of beam 
X -0063 2 = '844 X '0063- = "0000335 inch 2 gram. The corresponding increase, when 
the counterweight was added, was "844 X 0012 3 = "0000012 inch 2 gram. Applying 
these small differences to the observations of Experiment 12, if I may so far antici- 
pate, the torsional rigidity of the suspending fibre is changed from "0012577 to 
"001257736, so that if this had been overlooked, the error introduced would have 
been 1 in 35,000. It was not, as a matter of fact, observed until after the conclusion 
of Experiment 12, and then I placed one of the microscopes so as to see the edge of 
the lower hook of the beam, and measured the unexpectedly large deviations in the 
plane of the mirror ; those perpendicular to the plane I had always known to be 
practically inappreciable by the very small change in the position of the observing 
telescope needed to again see the scale reflected centrally. This insensible correction 
which tends to make G seem greater, can only be applied to Experiments 10, 11, and 
12, as the fibre met with an accident after Experiment 9, and was re-fastened to the 
beam. As it cannot be applied to the others, and is far smaller than the uncertainty 
of the experiment, it is not taken account of in the table. 

The rigid attachment of the gold balls to the mirror might seem to be purely 
imaginary, seeing that they hang from fibres 5 and 11 inches long, and so can lag 
behind when the mirror is subject to angular acceleration, that they must fly out 



NEWTONIAN CONSTANT OF GRAVITATION. 35 

owing to their centrifugal force when this acceleration has given rise to an angular 
velocity, and must be pulled by the gravitation of the lead balls so as to be further 
apart than supposed. Moreover, since each ball can rotate separately on its own fibre 
with a period of its own of as much as 6*720 and 9'055 seconds in Experiments 4 to 8 
and 10 to 12, they must, in their rotation about their own axes, lag behind the 
rotation of the mirror when it is being accelerated. The magnitude of these several 
errors is infinitesimal, or greatly below the limiting accuracy aimed at, and, in all 
cases, may be calculated and allowed for if necessary. Thus, in Experiment 8, the 
lower ball in the extreme case of an amplitude of 10,000 divisions, or 100,000 units 
(I make y^ division the unit, to avoid decimals), is at the middle of the swing thrown 
out by centrifugal force 2500000 inch, and the upper one about half as much. The 
linear acceleration on the balls, due to the action of the torsion fibre, is the same as 
that due to a pendulum nearly six miles long, or, more exactly, 364,335 inches, so 
that the actual acceleration produced by the fibre in the case of the lower ball is 
about 1 in 33,000 more than is supposed, and, on the upper ball, about 1 in 70,000. 
The amount by which the lower ball is pulled outwards by the gravitation of the lead 
ball next to it, even when that is in its neutral position, where its actual attraction is 
a maximum, is less than a ten-millionth of an inch. The rotational mobility of the 
gold balls, however, in Experiments 4 to 8 and 10 to 12, was more than I had 
intended, and, as I felt that it was important to know precisely what effect this 
would have upon the result, I referred the problem to Professor Geeenhill, who very 
kindly explained to me exactly how to evaluate it, and, with Professor Minchin, went 
through the great labour of obtaining and solving the resulting cubic equation. The 
rigidity of the fibre, in this the worst case, should "be diminished by less than 
1 in 7850. An increase in the thickness of the two suspending fibres of a few 
ten-thousandths of an inch, such as I made use of in Experiment 9, would reduce 
this to the order of ] in 100,000, or even less, and the complex calculation of this 
correction would no longer be necessary. 

Finally, it is assumed that the counterweight, when it has replaced the gold ball, 
is also rigidly connected with the mirror and acts axially. With respect to the 
rigidity of the attachment, it is unnecessary to do more than state that the friction on 
the suspending hook must be many thousand times greater than the greatest couple 
ever developed by the torsion fibre, and that, with regard to its axiality, the same 
remarks that were made with respect to the beam mirror apply with even greater 
force. There is only one point about which, in consequence of the microscopic 
examination after Experiment 12, I am not altogether satisfied. It seemed as if the 
hook suspension was not quite pendularly free so that the counterweight could rest 
hanging from the beam mirror at a very small angle to its natural position of verti- 
cality. This was not observable on the counterweight itself, but only by microscopic 
examination of the beam. Though the beam hook rarely varied in position by so 
much as '001 inch, I was able, by using great care in trying to make it rest in 

E 2 



36 PROFESSOR C. V. BOYS ON THE 

extreme positions, to introduce an uncertainty of position nearly four times as great. 
I cannot think that any serious discrepancy can have resulted from this, as the 
uncertainty of moment of inertia would be only a very small fraction of that found in 
the case of the beam mirror when the balls were suspended. This fault, such as it is, 
however, I intend to remove in my next experiments, from which I hope, also, to 
almost entirely exclude the small eccentricities already referred to. For this purpose 
I may either file the hook rather wider, or, as I think preferable, hang the counter- 
weight by a loop of silk, which will in no way constrain its hanging, but which will 
be rigid with respect to torsion. I wish, also, to make use of a slightly-silvered 
torsion fibre, so as to reduce the effect of electrical disturbances if they should be set 
up by the movements of the air. The square of the corrected period, with the 
counterweight on, differed more in Experiments 5 and 8 than it should have done, 
being 1702\35 in Experiment 5, and 1698'73 in Experiment 8. In order to see to 
what extent this discrepancy may have affected the result, I have calculated the 
rigidity of the torsion fibre in these two cases with the observations of this quantity 
reversed, that is, 169873 instead of 1702"35, and vice versd. The effect upon the 
result is 1 part in 10,600, so that if all the error is in one observation only, the other 
one is on this account alone less than 1 1 - in error. As any sticking of the counter- 
weight would tend to increase the moment of inertia, and hence the period, I am 
inclined to look with greater favour on the smaller observation, but the difference, in 
any case, is considerably less than the actual differences found in the final results. 

In connection with the beam mirror, it is convenient here to describe the means 
provided for keeping it under control from the telescope without entering the shielded 
corner of the vault. 

Below the apparatus, figs. 1 and 2, may be seen a tube terminating in a bent glass 
pipe which enters the hollow screw s. This is joined to a narrow piece of composition 
piping, which is carried across the interval between the two tables by the wooden bar 
which serves to protect the light driving cord, and, at the eyepiece of the telescope T, 
terminates in a mouthpiece. Where observations of deflection and period are being- 
made, ah - may be drawn through the tube causing a very gentle indraught through 
the tube of the window, fig. 12. This acting on one end of the mirror produces upon 
it a couple which may be employed to bring it to rest or to get up a swing of large 
amplitude. The extreme precision and delicacy of this process is best explained by 
considering an electrical analogue. The window tube, fig. 12, acts as a moderate 
resistance, the open space between the glass tube and the large hole in the screw as 
a short circuit or very low resistance, and the long tube across the room as a high 
resistance again. The electromotive force is the suction of the mouth. Owing to 
the high resistance of the long tube, but a feeble effect is felt at the glass end, and 
this is practically entirely satisfied by the low resistance leak. The available electro- 
motive force acting upon the resistance of the window tube is therefore very small, 
and in consequence the current acting on the needle is similarly minute. So delicate 



NEWTONIAN CONSTANT Of GRAVITATION. 37 

is this that it is quite easy by pinching the tube properly with the fingers to bring 
the movements of the mirror, when the counterweight but not the balls are suspended, 
down to one unit, corresponding to 75 o 000 inch movement of the gold balls if they 
were in their place. 

Conclusion of Part I. 

The apparatus and optical compass were made by the Cambridge Scientific 
Instrument Company. I cannot lose this opportunity of expressing my great 
indebtedness to Mr. Pye, who, in the absence of Mr. Darwin through illness, 
entered into every detail with the greatest care and faithfully carried out all the 
directions as to modes of construction upon which, after consultation with him, I 
finally decided. 

As already mentioned, Mr. Colebrook constructed the special tools and the very 
numerous extraneous apparatus. He also made all the special windows. Mr. Mtjnro 
made the tools for compressing the lead balls, and being his work they are of course 
accurate in the highest degree. Mr. Stanley undertook the large scale, but though 
the execution of the etching is excellent, the accuracy is not good. This, however, 
matters little, for the errors are eliminated by the calibration. 

The actual work of making the gold balls, the lead balls, the finish of the beam 
mirror, the quartz fibre work, the gilding and polishing of the inside of the central 
tube, and a great deal of the general fittings I did myself, either alone or with the 
help of Mr. Chapman and Mr. Colebrook of the Physical Laboratory. 

The apparatus, which belongs to the Science Collection of the South Kensington 
Museum, will, I hope, on the completion of the experiments, be set up in a special 
place in the Museum so that it may be seen in action by anyone interested. I intend 
to leave also permanently in the Museum a series of photographs of the apparatus as 
it appears in situ when each one of the operations is being carried out. Besides thiSj 
the note books and all the calculations will be left there permanently so that 
reference may be made to them in case any point is insufficiently explained. 

Part II. 

The Mode of Procedure. 

The actual method of carrying out the experiment, though in the main obvious to any 
one who has read the first part of this paper, is nevertheless in some particulars by no 
means evident. As, moreover, a careful explanation of the several operations and 
the purposes which they serve will make the mere numerical details of the actual 
experiments, which form the third part of the paper, more intelligible, I shall describe 
them in order, under distinguishing numbers. 

The operations, as described, are fourteen in number, but they are of very different 



38 PROFESSOR C. V. BOYS ON THE 

importance, and the time required for carrying them out differs also very much. 
Some few need only to be performed on the first putting together of the apparatus. 

Operation 1. 

After placing the instrument in the selected spot, with its centre tube vertically 
below the edge of the central overhead pulley, it is to be levelled accurately by 
placing a spirit level on the lid, and adjusting the levelling screws, until the bubble 
occupies the same position in the tube when the lid, carrying with it the level, 
is slowly made to revolve. Fix also the scale and large telescope in position. 

Operation 2. 

Hang up the lead balls by their wires and upper supporting pieces, pinning the latter 
to the thickened lower ends of the two steel bands. These are carried over the 
flat-rimmed pullies, and carry at their other ends counter-weights, so that the balls will 
remain suspended at any level. If the central tube is not in position the three readings, 
a, b, and c, fig. A, are made with the cathetometer, and thus the true distance from 
a to the centre of the lead ball, when the wire is stretched by the weight of the latter, 
is known. If, after one experiment, it is desired to make this measure, but not to 
move the central tube, since it is impossible to remove the lead balls completely, they 

Fig. A. 

Q- ' 



must be left suspended at such a height that the b of each is visible, This can be 
accomplished without taking away the lid and lid pillars, since they can be left 
suspended by their counterweight at such a height that the a of the (ultimately) 
upper ball is below the lid. while the a of the (ultimately) lower ball is above its lid 
pillar. Since all hang freely without touching one another, the «'s and b's can 
be determined, and on adding the known radius of the lead balls, the distances ah 
are known. 

Operation 3. 

Hang the gold balls by then" eye hooks upon a pin driven into any temporary stand. 
Measure with the cathetometer the three positions d, e, and/" of each, fig. B. From 



NEWTONIAN CONSTANT OF GRAVITATION. 39 

these the distances dg can be determined when the fibres are stretched by the weight 
of the balls. Also find their individual torsion periods by the method of coincidences, 



Fisr. B. 



1 



-d 



k::. 



-e 
-J 

watching them with the cathetometer telescope, and listening to the clock. This latter 
is needed for the purpose of calculating the very small correction (p. 35) which should 
be evanescent. The cathetometer measures can be made with an accuracy of two or 
three-hundredths of a millim., and this, as will appear when the figures axe 
examined, is more than abundantly accurate. 

Operation 4. 

Put the lead balls in the apparatus, fix the central tube in place, with its front 
window facing the scale, let the gold balls down the central tube, and hang them on 
the side hooks, place the lid in position ; having marked one side of the lead balls in 
some distinguishing manner (a very small spot of shellac varnish is what I used), 
suspend them with these marks pointing in some definite direction, e.g., inwards ; 
let down the mirror by its torsion fibre, and adjust the torsion head so that it hangs 
approximately centrally, and at a convenient height. 

Operation 5. 

Find, as already described, the division at which a perpendicular from the axis of 
the tube falls upon the scale. Twist round the central tube, if necessary, until the 
window reflects a light placed behind this division into the large telescope. 

Operation 6. 

Find the optical distance in terms of the corrected scale division from the silvered 
surface of the mirror to the foot of the perpendicular upon the scale, and thus find 
the angular measure corresponding to any observed deflection. 

The details of this process are sufficiently described under the heading The Steel 
Tape and its Accessories (p. 17). 

Operation 7. 

Make cathetometer readings of a, a and d, d. Subtract from these the corre- 



40 PROFESSOR C. V. BOYS ON" THE 

sponding quantities found in operations 2 and 3, ah and dg, and thus find the levels 
of the centres of the gold and of the lead balls. If the gold balls are on the whole 
high or low, lower or raise the torsion rod the necessary amount and re-measure 
a, a and d, d. 

Operation 8. 

If the mirror rests so that the foot of the perpendicular is about the position of 
rest as seen by reflection in the telescope, when the lead balls are, so far as it is 
possible to judge, in the same plane as the gold balls, all is ready for the next 
operation ; otherwise it will be necessary to turn the support of the torsion rod, which 
will not raise or lower it, until observation at the telescope shows that this is the case. 
The mirror will then be symmetrically placed with respect to the window. 

Operation 9. 

This is a long operation carried out with the optical compass, the object being to 
find the horizontal distances between the axes of the wires and between the axes of 
the fibres, to centre the torsion fibre with respect to the axis of the instrument, and 
to find the corresponding readings of the vernier of the lid and of the glass scale 
seen by reflection in the telescope when the plane of the wires and fibres is 
identical. Owing to the great length of this operation, the description of it is 
divided into sections. 

Section a. — Eemove the two pillars RR from the lid, and the first spur-wheel of 
the driving train W, which is made to simply lift off. Put the optical compass in its 
place on the lid so that the line of traverse is apparently parallel to the line joining 
the wires. 

Focus the positive eye-piece of each microscope upon its cross- wire or scale, and 
then shift the focussing collars c of each, so that when the microscopes change 
places in the same groove and are pressed up to their collars, they are each in focus 
on the same object. 

Section b. — Using one microscope in any one groove of one of the traversing slides 
T 1 or T 2 , focus alternately on the edges of the two wires, using the focussing screw 
S 3 to move both the same way, and turning the base of the optical compass upon the 
lid to move them opposite ways. When both are found in exact focus the line of 
traverse is parallel to the plane joining the axes of the wires. 

Section c. — Measure this distance. To do this the two traversing slides are placed 
together, and the fine steel spring passed through the hole in their Vs. The spring 
is then stretched and prevented from contracting by a pin passed through it at one 
end. The two slides T x , T 2 then are pulled together by the spring, but are separated 
more or less by the adjusting screw cone S 4 . The two microscopes are laid in the 
outer grooves (or the middle pair in case a 4-inch distance has to be measured), and 
the slides moved until each is directed upon one side of the corresponding wire. The 



NEWTONIAN CONSTANT OF GRAVITATION. 44 

final exact adjustments are easy of execution, for the focussing screw S 3 supplies a 
slow fore and aft motion, while the corresponding slow lateral movement is given by 
the screw cone S^ In order to allow one only of the traversing slides to move, the 
fingers of one hand are made to rest upon the slide which is to be kept still, and thus 
its friction on the base increased, the other one then only moves. When both 
microscopes are focussed upon (say) the right or apparent left sides of the wires, and 
their cross-wires are directed upon them also, the focussing slide is withdrawn about an 
inch, and the focussing block b put into its place. The slide is then pushed forward 
until the focussing screw rests against the focussing block. The small glass scale is 
then placed so as to rest against the two parallelizing screws S 3 S 2 , and against the 
micrometer screw S l5 and S 3 S 2 are moved until the scale is in focus in both microscopes 
at the same time. S x is then turned until the intended zero of the scale '04 is on 
the cross-wire of the left microscope and its head is read : it is then turned forward a 
fraction of a turn until a division at the other end of the scale 6'03 or 6'04 is on the 
cross-wire at that end. The amount of movement indicated by the head of the screw 
S l5 added to the tabulated distance from "04 to 6'03 or 6'04, is the distance from the 
right side of one wire to the right side of the other. If the eye-piece micrometer is 
used instead of the cross-wire, then '04 is brought in the central division of the left- 
hand microscope, and the micrometer readings of the divisions 6'03 and 6'04, or 6'04 
and 6 - 05, are taken in the right microscope. Knowing the tabulated length of either 
of these divisions and the number of eye-piece divisions corresponding to it, the 
amount to be added to the tabulated distance between "04 and the lower of the two 
observed, is readily found. The distance between the left sides of the wires is found 
in the same way, and the mean of the two is taken for the distance between their axes. 
The thicknesses of the wires ai'e also found by subtracting the readings of the apparent 
right from the readings of the apparent left sides, remembering that there are two 
whole turns of the screw. After each operation the focussing' block is moved round, 
and the focussing slide moved up so as to bring the wires into view. If they are not 
exactly on the cross-wire as before, the measure is rejected and a new one taken, but 
this is rarely the case. 

The example taken from Experiment 8 does not show the confirmatory observations 
made with the eye-piece micrometer, for at that time the micrometer scales had not 
been made. As I still rely upon the screw measure of the fractions and only take 
the eye-piece micrometer readings to satisfy myself that the screw observations have 
been correctly worked, this example will serve as well as a later one. 



MDCCCXCV. — A. G 



42 



PROFESSOR C. V. BOYS ON THE 
Measures of Wires with Optical Compass. 



Side. 


Wire. 


Scale. 


Head. 


Correction. 


Apparent right . 
left . 


. 1 Right 

Left . - . . . 

. ' Right (605+2) . . 
. Left 


603 
•04 ( + 4) 

603 

•04 ( + 4) 


641 

029 

955 
357 


+ •000025 



Apparent left side- 


Apparent right side. 


Thickness. 


Left. 


Right. 


6-03955 

•05357 


6-03641 
•05029 


•02357 

•00029 


•02955 
•00641 


5-98598 
5-98612 


5-98612 


•02328 


•02314 


Mean . . 5-98605 centre to centre. 
+ -000025 correction. 


5-986075 corrected valne. 



The (+ 4) after "04 indicates that when the right microscope was exactly on the 
division 6 "03, the left one was, by eye estimation, at "044, or -^ of a division above 
"04. Since also the screw-head reading has passed 1000, or a conrplete turn, and has 
risen in the two cases to 029 and 357, "05 is the quantity that must be written in 
the subtraction below to find the distances from side to side of the wires. 

(6 - 05 + 2) means that 6"05 was the division seen when the scale was put in its 
former place and that two whole turns of the screw were needed to bring 6 "03 into 
view again. It was because there was only one division at the supposed zero "04, 
that the scale had to be pushed forward so as to bring 6 "03 into view again, and 
•04 and G - 03 were used to measure the apparent left (but really right) sides of the 
wires. 

Section d. — Place the two microscopes in the centre pair of grooves and bring 
them both in succession to focus on the same wire, adjust the focussing collars, if 
necessary, so that when pushed up to their collars they are each in exact focus. 
Having the proper back window, figs. 13, 14, in position, withdraw the microscope 
and move the traversing slides till the microscope will be able to slide forward and 
view the fibres. Push both up to their collars and move laterally until the 
fibres are found. If, as is probable, they are out of focus, ascertain by moving either 
microscope by hand in its grooves whether the error of focus is in the same direction 
for both. If it is not, slowly turn the lid, using a lever bearing upon the pin of the 
first wheel of the train and entering 1 the nearest tooth on the edge of the lid. This 



NEWTONIAN CONSTANT OF GRAVITATION. 43 

does not affect the parallelism of the line of traverse with the plane of the wires, for 
the optical compass is carried round with the lid. When the fibres seem about 
equally out of focus and in the same direction, bring them towards or away from the 
microscopes, as may be necessary, by the adjusting screws of the torsion head. 
However carefully this may be done, the suspended beam and gold balls are sure to 
be set swinging slightly as a pendulum. This is easily overcome by resting a wax 
taper or very flexible piece of wood against the central tube, and while watching the 
motion in the microscope bearing very lightly upon it in time with the oscillations. 
There is no difficulty in reducing the motion to the xooo"o mca m a very short time. 
If a torsional swing has begun, there is nothing to be done except to wait until the 
amplitude is reduced to a very small amount. It is impossible to obtain real quiet in 
this sense, as owing to gravitation the observer's body and the gold balls will attract 
one another unequally. After one or two trials the two fibres wili be found 
simultaneously in focus, at any rate, if not continuously owing to the small torsional 
oscillations, yet between the elongations at successive half periods. I prefer to leave 
the apparatus at this stage and to return after an hour, when the mirror is more 
quiet, to verify the accuracy of focus. If this is correct since the focussing screw 
has not been touched, the plane of the fibres coincides with the plane of the wires. 
If more than a very small focussing correction is made, Operation 8 will have to be 
repeated afterwards. 

Section e. — Eead the great scale in the telescope and take the vernier reading of 
the lid. Then, since the wires and fibres are in the same plane, the lid reading and 
corresponding scale reading are known for one position, and, since the angular value 
of a scale division is known, also for all positions. 

Section J. — Measure the distance between the fibres and their thicknesses, using 
exactly the same procedure as described under Section c. I may mention here that 
as the beam mirror is only "9 instead of 1 inch as intended, the traversing slides as 
made would not come near enough together for both fibres to be seen at the same 
time. I therefore made use of the traversing slides in their other position, i.e., with 
T x to the right of T 3 instead of to the left, after having had the right side of T 3 
reduced by slot drilling so as to allow the now inner grooves to come j inch nearer to 
one another. The change from one position to the other is made in a moment. 



44 



PROFESSOR C. V. BOYS ON THE 
Example. — Measures of Fibres with Optical Compass. 



Edge. 


Fibre. Scale. 


Head. 


Correction. 


Apparent right . . 
left . . 


Right . . 
Left . . 

Right . . 
Left . . 


3-45 

2-55 (+ 7) 

3-45 

2-55 (+ 7) 


439 
078 

545 
180 


- -00033 



Apparent left edge. 


Apparent right edge. 


Thickness. 


Left. 


Right. 


3-45545 
2-56180 


3-45439 
2-56078 


180 
078 


545 
439 


•89365 
•89361 


•89361 


•00102 


■00106 


Mean . . 'S9363 centre to centre. 
— "00033 correction. 


•89330 corrected value. 



Section g. — Set one microscope to see one fibre and the other in the proper groove 
in the traversing slide to see one wire. Measure, as in Section c, the distance from 
one edge of one fibre to one edge of one wire. Then move the traversing slide so 
as to measure the corresponding interval on the other side. Knowing the two 
intervals, the thicknesses of the wires and of the fibres, and the distance between the 
axes of the wires (2 R), and between the axes of the fibres (2 r), it is at once known 
to what extent the pair of fibres are eccentric with respect to the pair of wires. 
Without touching the back adjusting screw of the torsion head, screw the other two 
until one of the fibres has moved the right amount as measured by the eyepiece 
micrometer. If a movement of more than a few thousandths of an inch is necessary, 
it is best to re-measure the right and left intervals, and again adjust. When this is 
done the two fibres are in the same plane as the wires and exactly half-way between 
them. 

If now the construction were perfect the torsion fibre would be in the axis of the 
instrument, and the lead balls would move centrally round it, but if either the two 
radii of movement of the gold balls r, r or the two radii of movement of the lead 
balls R. R differ from one another, or if the two lead balls hang from points which 



NEWTONIAN CONSTANT OP GRAVITATION. 



45 



are not diametrically opposed to one another, then the lead balls will not rotate about 
the torsion fibre as an axis. If, however, the optical compass is removed and the lid 
is turned round 180°, and the measurement repeated, then half the movement 
necessary to bring the fibres into focus as measured by the head of the focussing 
screw is the diametrical inaccuracy of the lead balls, and half the inequality of the 
right and left intervals is their eccentricity with respect to their mechanical axis 
measured in their own plane. The torsion head may now be moved half of each of 
these amounts separately, and then the vertical line half way between the pair of 
fibres, which by construction is necessarily the same as the torsion fibre within less 
than YoVo inch, is also in the mechanical axis about which the lead balls actually 
turn. 

Examples. — Plane of Fibres and Wires. 



Focus for wires, '05 on focussing screw. 
,, fibres, -25 „ „ 



■9. 



Therefore the fibres are behind (away from microscope) the wires by —, = '004 inch 



50 



Eccentricity of Pair of Fibres. — After setting the pair of microscopes to one 
interval and sliding to the other, the left appears in the eye-piece to be smaller than 
the right by about "007 inch. 

By measurement it is found to be '00792 less, or the pair of quartz fibres are 
•00396 out of centre. 

The necessary observations are : — ■ 



2)6 



Centre to centre, wires. 
Centre to centre, fibres. 



98607 
89330 
02314 Thickness right wire. 



90251 
00102 



Thickness left fibre. 



90149 



45074 Mean of right and left intervals. 

45470 Bight edge left fibre to right side right wire. 



"00396 Excess of right interval above mean. 
'00792 Right interval greater than left. 

Operation 10. 

Brepare for observations of deflection and period. Bemove the optical compass 
and replace the windows by fig. 12 at the back and fig. 11 in front. Place the 
tubular screens, fig. 1 5, in position. Screw in the pillars B, B, and arrange the guys, &c. 



46 PROFESSOR C. V. BOYS ON THE 

and counterweight so as to reduce the weight of the lids and balls and therefore their 
friction to a small amount. Place the first of the train of wheels W in place. See 
that the string operating the driving gear is in place, and that the india-rubber tube 
under the apparatus is connected to the composition tube going to the telescope. 
Place the two halves of the octagon house in position, and fill up the open gap where 
it overhangs the table at the back with a duster. See that the little electric lamp 
inside the house is properly placed to illuminate the vernier. Remove all superfluous 
apparatus from the table. Place the felt screen in position, and, when all is proved 
to be in working order, leave, if possible, for three days to acquire a uniform 
temperature. 

The angle through which the lead balls must be turned in order to produce the 
maximum deflection I had found in a preliminary calculation, completed before the 
apparatus was made, in which 2 R was made 6 inches, 2i' 1 inch, and the difference 
of levels 6 inches, to be 61° 15', and the effect of an error of 15' at this position to be 
1 part in 280,000. With the actual apparatus, in which 2 r is less than 1 inch, I 
found by experiment the angle of greatest effect to be 65°, which is that adopted. 
Knowing the vernier reading corresponding to the observed scale reading when there 
is no deflection observable with the optical compass, i.e., when the lead and gold balls 
are in the same plane, or in the neutral position, and taking this provisionally as a 
position of no deflection, move the lid in one direction through an angle of 65° by 
turning the handle of the wheel d by the telescope round 115 times. The exact 
setting of the lid is finally accomplished by lighting the electric lamp in the octagon 
house, and observing the vernier with the small telescope t. Three or more elonga- 
tions of the apparently moving scale are now read in the large telescope, and then the 
wheel d is turned 125 times back, and, when the mirror is approaching its position of 
rest, the remaining 105 turns are given to the handle, which leaves the balls 65° on 
the other side of the neutral point, and the mirror oscillating through 50 divisions of 
the scale, or even less. The vernier reading must be correctly set by the use of the 
electric lamp, little telescope, and handle d, as before. Three or more elongations are 
ao-ain taken. The elongations are corrected, and from the corrected elongations the 
positions of rest, when the lead balls are in their -f- and in their — positions, are 
calculated. If the supposed neutral position had been accurately found, its scale 
reading would be exactly half way between the + and — position of rest. If, as is 
probable, it is .not quite accurate, then, since the variation of the position of rest 
of the mirror is hardly observable when the lid is moved even so much as 1° from its 
position of maximum effect, while such an uncertainty of position is not possible in 
the provisional setting, all that has to be done is to bring the lid into such a position 
that the mirror is at rest exactly half way between its extreme + and — positions 
already observed. It is not sufficient to move the lead balls through an angle 
corresponding to the error, because, though at the neutral position the smallest 
variation produces the greatest effect upon the gold balls, they do not follow it abso- 



NEWTONIAN CONSTANT OF GRAVITATION. 47 

lutely. I always take two observations with the telescope of the position of rest of 
the gold balls when the vernier readings differ by about 2° at the neutral position, 
and thus, knowing how many soale-divisions deflection are produced at this position 
by a movement of the lead balls of 1°, I am able at once to find the vernier reading of 
the true neutral position (N). Then, when the vernier reading is made N + 65° or 
N — 65°. the deflections in the + and — directions are found to be the same within 
■jTj- per cent., from which it is evident that the + and — positions have been set 
truly, with a superabundant degree of accuracy. This preliminary determination I 
generally make the night before the deflections and periods are determined, which in 
Oxford is best done on Sunday night between midnight and 6 A.M. The daytime, of 
course, is out of the question, owing to the rattling traffic on the stones in St. Giles', 
about a quarter of a mile away ; and all nights except Sunday night the railway 
people are engaged making up trains and shunting, which is more continuous and 
disturbing to the steadiness of the ground than a passing train. Even these come 
through at intervals on a Sunday night, and this limits the accuracy with which the 
periods can be observed. All having been prepared for the Sunday night during the 
previous week, the room is shut up all day, and at midnight or a little later the 
actual observations of deflection and period are begun. 

For a long night's work without accidents, I am able to take two or three sets of 
observations alternately at each of the -f- and — positions, with one at the neutral 
position ; one period at each of the -f and — positions, lasting about 45 minutes, and 
occasionally one at the neutral position, lasting about 15 minutes, and finally two or 
three sets alternately at each of the + and — positions, followed rarely by one, or 
even two, periods of 30 to 45 minutes. For each set of observations at the + and 
— position, I observe six consecutive elongations, and sometimes eight if I am 
disturbed by the trains. I do not begin them until the apparatus has quieted down 
from any very small tremor which the rotation of the lid may have set up. 

In observing the period, the point of rest is known from previous observation. 
A conspicuous pointer tapering to a point, which can be inserted into any division, 
or if between can be read to a tenth of a division, is placed at the point of rest. 
Air is gently drawn from the mouthpiece for a quarter period and then stopped. 
According to the speed at which the pointer flashes past I determine whether or not 
to draw air again. If I do, I begin about a quarter period after the transit, and 
continue until the next transit, or a quarter period longer still, according to the 
velocity of the transit. It is most important not to begin or leave off drawing the 
air suddenly, lest a quick period movement, of which there are five independent of 
one another, should be set up in the mirror. I begin very gently, gradually increase 
and gradually leave off, the result of which is a beautifully steady motion of the 
mobile system, extending far beyond the limits of the scale. I then start the 
drum and make a dozen marks with the key in rapid succession, to indicate the 
beginning of an observation. At each transit, the key is pressed suddenly and then 



48 



PROFESSOR C. V. BOYS ON THE 



Fig. C. 



__L_J I I I I J L_J_L 



I I I I I I l i I I l l II 1 I I I I I I I I. _L_1 I I I I I I I 1 



I I I I I I I I I I I I I I I I 



J I I 1 1 I I I 1 L 






I I I I I I I I 1 1 l I I I I 



J-.,J— I ! I i i i I i J... I I I— 1_ L_-L_J-.,L. I 



i I I I I I il L_J_ 



26- 



i I I i_ I I i i I l_.i i I i i i i i i i i i i i i I i 



' ' ' ' I I '■ i ■ ' 



-i—i I I I l_ 



-J-L-IniL 



4—1— J I ' 



1—1 I) I L 



— I • 1 ' L J_ 



J I 1 I 1. _l i—l I l_J I 1 1 ft— J 1 I 1— J I I I, 



'_ L -' ' ± .J _ .!_ 1- '.._L J . ..LJ ' t i | ill _» ■ j_ i. I 1 i 



| i -J i_ i i i . L— '.- L_ J_ 



_l L— ! L I 1 1 I I I I I I 1 L-l— I I I -U 1 I I I I L 



- 1 __ 1 !_ J 1 L— I 1. . 



NEWTONIAN CONSTANT OF GRAVITATION. 49 

held down for one second, which produces a "transit mark," the purpose of which is 
to indicate that the previous dash was made at a transit of the pointer. Immediately 
afterwards I note in the hook an arrow showing the direction of motion. Every 
transit is thus marked during the first stage, which lasts 10 or 15 minutes. In order 
to know the actual time of any of the minute marks, I hold the key down once at a 
minute for six seconds and thus produce " time mark." This also is noted in its 
proper place in the book with the time. To still further make sure of the place in 
the book which corresponds to any place on the smoked drum, I occasionally make 
a "castle mark," that is, hold the key down during alternate seconds four or five 
times, and note that also in the book. The proper sequence of time marks, castle 
marks, and transit marks, is sufficient to make it evident afterwards to which arrow 
in the book any particular transit mark belongs. During this stage it is not possible 
to take the elongations as they are off the scale. I then leave the apparatus to itself 
for about 20 minutes after first stopping the drum. On my return I start the drum, 
secure another time mark, and every transit, as before, with a castle mark somewhere 
for distinction, but now the elongations being observable I note them in the book at 
the same time. Following the practice of Professor Cornu,- but on an extended 
scale, I take the transits of the chief divisions at first of every 1000 divisions, then 
of every 100, and after a time of every 10. These are distinguished on the drum by 
four rapidly repeated dashes after a 1000, three after a 500, two after a 100, one after 
a 50, and none after a 10. I cannot take single divisions as they pass by so rapidly. 
I have not used these marks except in rare instances, but they are available for 
reduction in case time for the very tedious calculation could be found. Fig. C is 
a full size reproduction of a portion of the sheet of October 1st, 1893, after I had gone 
over it and scratched in the actual times. The different classes of marks are all to be 
seen. I do not, as a rule, find it possible to put in arrows while writing elongations, 
and marking transits of divisions as well as of the pointer. Their existence is 
understood between elongations. In addition, I generally place a letter or word 
to distinguish good observations of transits from bad, thus: — ► g., *— v.g., -- bad, 
or — ► "04 i late. I do not think the v.g. observations can be more than '01 second 
in. error, or the g. more than '02 or "03 second. Those unmarked might be perhaps 
as much as - 1 second, though they may also be good, but those marked bad would 
probably be more. If it were not for the high period tremor set up by the trains, 
which prevent good observations when the amplitude is less than about 40 divisions, 
I should expect to obtain a higher degree of accuracy in the periods than are actually 
obtainable. I sometimes take observations of deflection and period on more than one 
night. 

Operation 11. 

Transfer the gold balls to the side hooks, and leave for a day, if possible, to quiet. 
Find the deflection, if any, produced upon the mirror alone, by moving the lid and 
JIUCCCXCV. — a. H 



50 PROFESSOR C. V. BOYS ON THE 

lead balls from the -\- to the — positions. Find also with large amplitude, the exact 
period with and without the counterweight, using the drum and following all the 
details given in operation 10. At this stage it is convenient to set up the 
cathetometer and measure the stretching of the torsion fibres by observation on the 
bottom hook of the mirror. This is not necessary for the purpose of finding G, but 
it is of interest as bearing upon the elastic properties of quartz fibres. 

Operation 12. 

Turn the lid round to the neutral position. Place the steel bands on the flat- 
rimmed pullies. Pin to the ball holders, and hang on at the other end the 
counterweight. Raise the balls about -§- inch, turn them individually through 60° and 
let the geometrical clamps down through the triangular orifices of the lid pillars, 
until the balls rest on the india-rubber rings. on the base. Paise the lid, leaving it 
balanced in the air by its counterpoise, and after removing the two counterweights 
and the holding pins, take away the steel bands. Let down the lid again. Partly 
balance it as before. Put screens and octagon house in position as before, and after 
a day or two take deflections, if any, when the lid and lid pillars are moved between 
the + and — positions. Three sets of six elongations at least should be taken at 
each position. 

Operation 13. 

Pe-suspend the gold balls in the same position as before, and find the deflection of 
the mirror, if any produced, by moving the lid and lid pillars from the -f- to the 
— positions. 

Operation 14. 

Take the focussing collar off one microscope of the optical compass, and slide it on 
to the nose end of the other, so as to raise it high enough to see the side of the 
bottom hook of the beam mirror. Pernove the front lens of the object-glass, which 
reduces the magnifying power to rather less than one-half. Set the optical compass 
so that the vertical tangent to the curve of the lower hook is on the zero of the 
micrometer scale in the eye-piece, that is when the mirror alone is freely suspended. 
Hang on the counter-weight and take the scale reading. Hang on the gold balls 
instead of the counter- weight and take the scale reading again. The object of this 
is to find to what extent, if any, the axis of rotation of the beam changes when the 
balls or the counterweight are suspended (see p. 34). 



NEWTONIAN CONSTANT OF GRAVITATION. 



51 



Part III. 

The calculation of the results from the figures obtained by observation is divided 
into four sections : — (l.) The deflections and periods ; (2.) The geometry of the 
apparatus; (3.) The dynamics of the moving system; and (4.) The combination of 
these resulting in the determination of G, the Newtonian constant of gravitation, 
and indirectly of A, the mean density of the earth. In the preparation of this part 
I have been greatly helped by Mr. S. G. Starling, of the Royal College of Science, 
who has carried out the laborious numerical calculations. 

1. Tlie Deflections and Periods. 

The treatment of the figures obtained during the observations of deflection will be 
best explained by an example. I give two consecutive sets, one the worst obtained 
the whole night, and the other a particularly good one, but others obtained that 
night were practically as good. 

Sept. 17, 1893. 



A = 150°-9. 


13h. 


0m. 


15°-15 C. 




24907 


-24 


24883 


716 




390 


24493 


24193 


-26 


24167 


598 


•835 


326 


24493 


247S9 


-24 


24765 


499 


■834 


271-5 


24493-5 


24292 


-26 


24266 




•838 






* 






418 




226 


24492 


24709*f 


-25 


24684 


354-5 


•848 


1923 


(24491-7) 


24355f 


—25-5 


24329-5 


298-5 


•842 








24654+ 


-20 


24628 








24492-9 



A = 


20°-9. 


131i. 


15m. 


15°- 


L5 C. . 




19888 


-19 


19869 


1702 




926-4 


20795-4 


21591 


-20 


21571 


1425 


•8373 


775-3 


20795-7 


20165 


-19 


20146 


' 1194 


•8379 


649-5 


20795-5 


21359 


-19 


21340 


1001 


•8384 


544-5 


207955 


20358 


-19 


20339 


839 


•8382 








21197 


-19 


21178 








20795-5 



* A short period oscillation or tremor, set tip probably by a passing train. 
f A pendnlar oscillation, set np probably by a passing train, 

H 2 



52 



PROFESSOR C. V. BOYS ON THE 



A represents the lid reading differing from 8 5 "9, the neutral position, by the 
azimuth 65° of the lead balls. The actual time of the beginning of a set is next 
marked and then the temperature of a thermometer set up close to the apparatus. 
This is illuminated and read by the same means that are provided for reading the lid 



vernier. 



The first column of figures are observed elongations expressed in tenths of scale- 
divisions. The second column contains the scale corrections, in which are included 



Fig. D. 



2450 



+ position 



244 9 



2080 



-position 



2079 





















































































































































































































• 


































£ 








i »0 


















•< 








3 




n u 


































o 






















>c 




















































































































^^ 














a 










Interval of 30ft. 


Sin. 


■ "— i—*— — S^L-J 






































































































"" 












































































m 






































































IV i 








































• 














»r 




i 











































































































































12 



13* 



14- 



15 



10' 



both the calibration and the circular errors. The third column are the corrected 
elongations, the fourth the differences of these or amplitudes, the fifth the ratio of 
these or the decrements, in the sixth are the quotients of each amplitude by 1 -f- the 
following decrement. The last column contains the algebraical sums of the corre- 
sponding numbers in the third and sixth columns. They represent the points of 
rest during the course of the oscillation. Each series gives a mean point of rest of 
which a dozen or more may be obtained in one night. I prefer to arrange all the 
individual points of rest as well as the mean points in their proper places in a 
diagram, of which abscissa? represent the hour and the ordinates the points of rest, 
but on a very large vertical scale. The one of these for the evening's work chosen 
for illustration is shown in fig. D, from which it will be seen that a gap of 368 inches 
has been cut out to save room. The series of mean points of rest are shown in the 
following table : — 



NEWTONIAN CONSTANT OF GRAVITATION. 



53 







Position. 




Time. 
















Neutral. 


Positive. 


Negative. 


h. m. 








12 32 


226499 






12 46 






20797-3 


13 




24492-9 




13 15 






20795-5 


13 30 




24491-3 




13 43 






20795-1 


13 57 




24492-5 




Oscillation of large amplitude for period. 


15 2 






20793-7 


15 15 




24492-2 




15 2L (?) 






20795-2 


15 42 




24490-2 





The deflections P are obtained by taking these in groups of consecutive threes, to 
allow as far as possible for steady creeping of the zero. It will be seen that in the 
present instances there is nothing very definite that can be attributed to this. 

The four deflections obtained in this way before the time interval are — 

3696-5 
3696-6 
3696-0 
3696-8 



The two after are — 



(36977) 
3696-0. 



As the mean point of rest 20793'7 was taken immediately after the oscillations of 
large amplitude produced by the air draught and was definitely slightly disturbed, 
I have not included the resulting deflection 36977 in the series from which the true 
deflection on that particular night was determined. The agreement is exceedingly 
close, so that the mean of the five values P = 3696 "4 may be taken with considerable 
confidence. 

The observations on this night were rather more consistent than usual, owing, as I 
believe, to the very unusual quiet noticed at the time. 

I only took one observation of period on this night, z-ecorded as follows : — 



54 



PROFESSOR C. V. BOYS ON THE 



A = 150"-9. Pointer at 24520 Drew air once. 

-27 



24493 No time correction worth making. 



Times c 


if Transit 












h. m. 


s. 










14 20 


36-34 




— ► g\, time mark, 14h. 21m. 






22 


13-1 




. O', 






23 


49-7 + 


•02 


— ► -02 early. 






25 


26-58 - 


•06 


<-- -06 late. 






27 


3-01 




— > v.g. Castle mark. 






28 


39-68 




Interval. 






41 


32-7 




<— Time mark, L4h. 42m. Castle 


mark. 




43 

(44 


9-42 
46-1) 




— v.g. 

< — Pendular oscillation. 


Amplitudes. 


Points of rest 








26915 - 26 "" 




•ji 


24491-2 


46 


22-87 








4406 1 










22505 - 22 


All bad with 




2448S 


47 


59-42 






- pendular dis- 


3690 | -g 










26199 - 26 


turbance 


% ft 


24486-6 


(49 


36-1) 




Bad transit 
23106 - 24 _ 




3101 I o 

CD rt 

a 




51 


12-48 




25698 - 25 Castle mark. 


2601 " 




52 


49-35 




Transit. 









If the pointer had been found to have been definitely out of place, but, of course, 
by a small amount, I should have corrected the observed times of transit by a series 
of alternate + and — quantities, calculated from the amplitude, period, and error of 
position. In the present case, owing to disturbance, the point of rest showed an 
uncertainty of nearly half a division, and I could not be sure from these observations 
that the pointer was not placed that much in error. On the other hand, after 
subtracting the time of each transit from that above, the series of observed half 
periods show a small, fairly regular, increasing and alternating second difference, 
which is in itself a sign that the pointer was very slightly on one side of the true 
position of rest. If no account is taken of this, the half period deduced from the 
first and last observation is found to be 

96*650 seconds ; 

from the first observation marked g to the last marked g it is 

96*649 seconds ; 



NEWTONIAN CONSTANT OF GRAVITATION. 55 

and if the times of transit are corrected by one quarter of their second difference, so 
as to approximate to the times of transit of the point of rest, the half period over the 
whole series becomes 

96-645 seconds. 

The object of examining so many transits is not so much with the idea of applying 
methods of least squares or of otherwise equalising errors, but mainly to see that the 
oscillation is going on regularly and that no sudden disturbance has aiisen which, if 
it were undetected at the time, might become lost and yet leave the result in error 
by an observable amount. I find that in the present instance I did not try to improve 
upon the observations by arithmetical manipulation, and that 96'650 was taken as 
the observed half-period. Two small quantities had to be subtracted from this, one a 
correction of — '0034 due to a gaining rate of two seconds a day of the clock, and one 
of — '1508 on account of the damping effect of atmospheric resistance. The true 
whole period for no damping then becomes 192'992 seconds, and its square 37245 - 9 is 
the quantity which is finally made use of in the dynamical calculation. It is recorded 
as T B 2 , the square of the time with the balls on. In a similar manner T c 3 is found 
when the counterweight is on, and T 3 when the mirror alone is swinging. 

Under this heading the deflections produced in Operations 11, 12, 13 must be con- 
sidered. The deflection in Operation 10 is due to four possible attractions : — 

(1.) Lead balls, &c, on gold balls. 

(2.) Lid and permanent fixtures, &c, on gold balls. 

(3.) Lead balls, &c, on beam mirror. 

(4.) Lid and permanent fixtures, &c, on beam mirror. 

The deflection, if any, of Operation 11, is due to (3) and (4) above. Similarly the 
deflection produced by Operation 12 is due to (4) alone, and of Operation 13 to (2) 
and (4). Knowing, therefore (1) + (2) + (3) + (4) ; (3) + (4) ; (4) ; and (2) + (4) ; 
(1), (2), (3) and (4) are separately determined. 

I have on two occasions since Experiment 3 was completed (which was of a semi- 
provisional nature) carried out the deflection observations of Operation 11. On 
September 1, 1893, 1*5 units or "15 division was obtained. There was a very slight 
+ creep. On September 11, with no creep and very consistent behaviour, - 5 unit or 
•05 division was obtained. I do not know whether I should take "5 or 1 unit. The 
difference is beyond what can be observed with any certainty. 

I find that the lid was turned 180° between the two experiments, but this could not 
make any difference. I have taken I unit as the deflection in Experiments 4 to 12, 
and have calculated what it should be in Experiment 3. 

Most careful observations on September 2 and 3, 1893, failed to show any deflec- 



56 PROFESSOR C. V. BOYS OX THE 

tion under Operations 12 and 13 ; certainly not 1, and not, apparently, "1 unit. 
From tins it will be evident that since 

(3) + (4) = 1, 

(4) = o, 

(?) + (4) = 0, 

(2) = 0, (3) = 1, and (4) = 0. Therefore 1 unit must be subtracted from the 
observed deflection of Operation 10 in all experiments after No. 3. It. is for this 
reason that the numbers under P in Table I., p. 63, differ very slightly from the 
observed deflections. 



2. The Geometry of the Apparatus. 

In this part of the calculation I find the exact relative positions of the several 
gravitating bodies, from which the couple twisting the fibre may be found in terms of 
G. Thus, the couple — - QG. As before, the process followed will be most readily 
explained by giving an example. 



NEWTONIAN CONSTANT OF GRAVITATION. 



59. 



Experiment 8. 



8 = 65° - 22' = 64° 38' 
R H = R r = 299304 
r a = r L = -446650 

log r — 1-6499673 

p =rR sin' e = 2-704465 
b = R cos 9 = 1-232247 
b-r = -835597 

b+r = 1-728897 



sin 64° 38' = -9035847 
cos 64° 38' = -4284095 



p* = 7-314131 

(b-r)°~= -698222 
(6 + r)« = 2-989085 



7i L = -0321 V = 


•001029 


7i H = -0516 


V = -002660 


H L = 6-048339 H L 2 = 


36-582411 


H H = 6-02885 


H H a = 36-347032 




Low. 


High. 


Low. 


High. 


f- 


7-314131 


7-314131 


p" 7-314131 


7-314131 


(b - ,-y 


•698222 


•698222 


(b + ry 2-989085 


2-989085 


¥ 


•001029 


•002660 


II 2 36-582411 


36-347032 


D2 


8-013382 


8-015013 


46-885627 


46-650248 


logD 2 


•9038157 


•9039042 


1-6710397 


1-6688539 


logD 


•4519078 


•4519521 


•8355198 


. -8344269 


logD 3 


1-3557235 


1-3558563 


2-5065595 


2-5032808 


log p 


•4320814 


•4320814 


■4320814 


•4320814 


log jd/D 3 


1-0763579 


1-0762251 


3-9255219 


3-9288006 


logM 


3-8696230 


3-8696634 


3-8696230 


3-8696634 


log m 


■4234097 


•4234163 


•4234163 


•4234097 


log >- 


1-6499673. 


1-6499673 


1-6499673 


1-6499673 


log couple 


3-0193579 


3-0192721 


1-8685285 


1-8718410 


Couple 


1045-580 
1045-371 


1045-371 


73-880 
74-446 


74-446 




2090-951 


148-326 






148-326 








Q = 


= 1942-625 





In order to determine the moments of the attractions of the large balls M, M 
upon the small ones m, rn, the distances represented in figure E by 'p and r, and 
the true distances D between M, M and m, m are required, also the masses M, M 



mdcccxcv. — A. 



58 



PROFESSOR C. V. BOYS ON THE 
Fig. E. 




and m, m — that of displaced air. Then the moments are for any one attraction 

out of the four possible. 

GtMmpr 



D 3 



These are most readily obtained from the observations in the manner set forth 
on the last page, where every figure made use of is set down. Single multiplications 
are performed on the arithmometer more quickly than by logarithms, hence natural 
sines and cosines are employed. Continued multiplications are more conveniently 
performed by logarithms, and the change from D 3 to D 3 can only be so effected. 

The angle, 6, is the amount through which the lead balls are turned from the 
neutral position — the angle through which the gold balls are deflected. 

R, the radius of motion of either lead ball, is half the distance between the axes of 
the wires, and they are taken in the calculation as being identical, i.e., there is 
supposed to be no eccentricity. In Experiment 5 I calculated the result both on 
this supposition and more laboriously giving the true and slightly different values to 
E, H and R L , the radius of motion of the upper and of the lower ball respectively. The 
difference in the result only amounted to 3 parts in 2,000,000, and so, as I explained 
on p. 26, a small eccentricity, if it exists, is of no consequence. 

r, the radius of motion of either gold ball, is half the distance between the axes of 
the fibres. The next few lines explain themselves ; they simply give intermediate 
quantities required for the solution of the different triangles. h L and h B are the 
differences of levels of the centres of the lower gold and lead balls and upper gold and 
lead balls respectively. H L is the difference of level of the lower lead and upper gold 
ball and H H the other great difference of level. The four couples obtained are those 
due to the attraction of the two pairs at the same level and of the two pairs at 
different levels. The latter are in the opposite direction to the former, and are 
therefore subtracted. The result, 1942*625, when multiplied by G, is the actual 
moment produced upon the torsion fibre by the action of the balls upon one another 



NEWTONIAN CONSTANT OF GRAVITATION. 59 

upon the supposition that the balls are all spheres, and act as if they were concen- 
trated in their centres. The brass ball holders, as already explained, cause the forces 
to be actually more than they appear to be, on the assumption that the lead balls act 
as if they were concentrated in their centres, so that 1 + "0001366 is the factor by 
which the couple must be multiplied to correct for the brass ball holders. The 
corresponding correction for the gold ball holder is only 2Tooo"o 0I> the whole. One 
small correction, too small to matter, but which I have calculated with some labour, 
is the stability due to the gravitation of the table. This introduces a restraining 
couple upon the balls alone in Experiment 8 of -axoboo oi " the whole. Finally, there 

is the correction already mentioned on p. 31 of _„„ nnn on account of the attraction of 

J *■ 26o,000 

the gold ball for the wires and the lead ball for the fibres. Combining all these, 
the actual couple developed is found to be equal in Experiment 8 to 1942'882 

inch 3 gramme 

■ — - — units. 

second- 

3. The Dynamics of the Moving System. 
As before, I shall take my example from Experiment 8. 

Moment of inei'tia of counterweight No. 3 or C . . = '0163120 

T B 2 37245-9 T B 2 -T C 2 

35547-17 

T c 2 1698-73 

T 2 not taken. 

Moment of inertia added to beam when balls are placed in position, called B. 

f balls translated 5-302804 X -44665 2 =1-0578893 

I + hooks translated 0-1190 X -379 2 = '0017093 

B j + balls rotated -4X5-300252 X -126134 2 = '0337303 

|^+ hooks rotated -012 X -025 2 = -0000075 

B = 1-0933364 

C = -016312 



B-C 



= 1-077024 



_ By - CT, 



V - T c 3 



•0351565, 



S = y B -? = -001196138. 

1 2 



60 PROFESSOR C. V. BOYS ON THE 

The moment of inertia of the counterweight is directly obtained from its dimen- 
sions. The moment of inertia added to the beam requires more explanation. When 
the balls are hung on to the beam in the manner already described, they add to its 
moment of inertia, both on account of their distance from the axis, and on account 
of their own moments of inertia, about their own axes. Besides the balls the small 
wire hooks and the quartz fibres produce their own effects. These are found in the 
four lines bracketed B. In the first line the mass of the balls is made up as 
follows : — 

Mass of gold balls + wire holders, corrected for 
buoyancy as against brass weights, but not 
absolutely, -f- | mass of displaced air . . . . 5'302204 

+ mass of quartz fibres "00060 

5-302804 

this is multiplied by the square of the radius r. 

In the second line the radius of the support of the hook is obtained by direct 
measurement of the beam itself. It is relatively unimportant. In the third line the 
mass of the balls does not include the ball-holders or fibres or (perhaps wrongly) that 
of any surrounding air. The radius of the ball is found by a screw micrometer. The 
fourth line needs no explanation ; it is infinitesimal. 

U is found from the formula placed next to it. This is the moment of inertia of 
the mirror. It is not required in the calculation, but is found for the purpose 
of comparison. It should be constant. 

S represents the stiffness of the torsion fibre, i.e., the couple that must be applied 
in order to twist it through unit angle (57°"296). 

If the unknown moment of inertia had been eliminated by the usual method, that 
is by supposing the torsion constant while the mirror was made to swing either with 
or without a known added moment of inertia (in this case, that due to the balls) then 
T B 2 and T ~ would have been required. Taking T,/ from the previous experiment 
when it was found to be 1168 - 00, 



and 



BT 2 

U becomes . ° a = '035396 

J-b" — J-o 

S becomes ^" B , = -001196375. 



Since the torsion is not the same when T B 3 and T 2 are being found, as in one case 
the fibre is much more strongly stretched than in the other, and is therefore longer 
and thinner, and is not necessarily made of a material having the same rigidity, the 
above figures are spurious. They differ from the true figures found in the previous 
page, but U, which is eliminated differs far more than S, which is made use of. The 



NEWTONIAN CONSTANT OF GRAVITATION. 61 

reason of this is made clear if a correction, 6 in terms of S, is included in the expres- 
sions for U and S. Since the fibre becomes stiffer when the balls are taken off, it is 
simpler to consider this correction as a stiffening of the fibre when it is unloaded 
instead of the reverse when it is loaded. The expressions are now : — 

u= BT o Ml + 0/S) 



s = 



T B 2 - T ~ (1 + 0/S) ' 

4tt 2 B 
T B 3 - T 3 (1 + 61$) 



It now appears that in both, the denominator is affected to the same extent, which 
is very small since T 3 is small compared with T B 3 . On the other hand the numerator 
of S is not affected, while the correction applies to the whole numerator of U. 

The very great effect of this upon the absolute value of S is well shown in Experi- 
ment 9, where the additional weight was 7"975 instead of 5"314 grms. In con- 
sequence of the extra amount of stretching S fell from '001196 to '001147, or nearly 
5 per cent. The actual elongation of the torsion fibre in the two cases was '0394 
and '0677 inch. The whole length of the fibre was 17 inches, so the amount of 
stretch was '232 and "398 per cent. Even if the volume of the fibre remained 
constant the diminution of torsional rigidity could not be accounted for with a 
material of constant rigidity. This point is perhaps worth considering in connection 
with Poissojsi's ratio and the theory of elasticity, more especially in consequence of 
the great hardness, freedom from structure and possible elongation without per- 
manent deformation or change which are met with in a quartz fibre. I must, however, 
defer its discussion for the present or leave it to some one more competent than 
myself. 

4. The Combination of the preceding Three Results. 

The method of combining the results given in the first three sections of this part 
is simple enough. From the first section, the deflection in scale divisions when the 
lead balls are moved from the + to — positions is obtained. Let this be called P. 
The second section gives Q the numerical coefficient of G ; thus, Q G is the couple 
exerted upon the fibre. From the third section, the actual couple S that would be 
needed to twist the torsion fibre through an angle of 1 unit (57°'3) is obtained 
without any reference to G, and D being the actual distance in units or tenths of a 
scale division from the scale to the mirror measured as explained on p. 17, it follows 

G = PS/4QD. 

The 4 in the denominator is due to the doubling of the angle by reflection and to 

the doubling of the deflection by moving the lead balls from the + to the — positions. 

G is thus obtained in inch 3 /gramme second" units ; to convert it into 



62 PROFESSOR C. V. BOYS ON THE 

centimetre 3 /grarmne second 3 units it is merely necessary to multiply by 16"3861, the 
number of cubic centimetres in a cubic incb. 

To obtain from this the density of the earth I might have recalculated the 
attraction of the earth treated as a rotating ellipsoid composed of similar shells of 
equal density as given in Professor Poynting's paper, but since it is obvious that 
G A is a constant, and is, taking Poynting's figures, equal to 367970 X 10" s , it is 
merely necessary to divide this figure by G to find A. 

Again, taking Experiment 8 to furnish an example, these operations are as follows : — 

G = « = /^r^- = ^^ x "- 

4QD 4 x 1942-882 x 13996o 

in inch 3 /gramme second 2 units. 

Multiply by 16-3861, then G = 6"6579 X 10~ 8 in GG.S. units, and A = 5-5268. 

The more important quantities of the whole series of experiments are exhibited in 
Table I, which, as the heading shows, is constructed on the Inch, Gramme, Second 
system, in conformity with the actual measurements. The supplementary table is a 
repetition of the most important quantities in C.G.S. units. Here below the constant 
of gravitation G is to be found the series of values of A the mean density of the 
earth. Appended are Cornu's and Poynting's values, Cornu's G being obtained from 
his A in the same way that I obtained my A from my G. 

An examination of the table shows that I have employed a fair variety of con- 
ditions, the lead balls alone being unchanged throughout the series. Three pairs of 
small masses were made use of. The lead balls were practically unchanged in 
distance, though, after Experiment 7, they were brought nearer together by -^ inch 
about. The effect of this on the deflection P and the couple Q is at once evident in 
Experiment 8. Three fibres were employed, though, as already mentioned, the 
rigidity was very different in Experiment 9 owing to the great longitudinal strain. 
The different torsional rigidities are tabulated under S. 

The periods are tabulated under their squares, i.e., after correction for damping. 
T B e is with the gold balls or cylinder suspended from the mirror and with the lead 
balls at a + or — position, wdiere, by producing a maximum couple, they do not 
affect the period. T x ~ is the corresponding period with the lead balls in their neutral 
position where they accelerate the period. I might, following Reich, have inde- 
pendently calculated G from the acceleration produced in this way, but these periods 
were not determined with the same care as the others, and in any case, the difference 
is too small for an equally accurate result to have been obtained. T c - and T ~ are the 
square of the periods with counterweights and with nothing on the mirror. 

The pairs of quantities tabulated under H L H and 7? L H are the four differences of 
levels between the lead and gold balls. Thus 6*0296 in Experiment 5 is the 

* 36954 = 36964 - 1. See p. 56. 

t -00119598 = -00119G13 (1 - 1/7850). See p. 35. 



NEWTONIAN CONSTANT OF GRAVITATION. 



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64 PROFESSOR C. V. BOYS ON THE 

difference of level of the upper lead and lower gold ball, while 6*0139 is the corre- 
sponding difference between the other pair. Similarly "0059 is the difference of level 
of the upper lead and upper gold balls, and "0216 the difference of level of the lower 
pair of balls. 

In order to eliminate as far as possible any systematic errors that might arise for 
instance from imperfections of the copper central tube, which of course is very near 
the gold balls, or from want of perfection in the lead balls, though nothing comparable 
with the error of experiment need be feared on this account, I made some change in 
the circumstances after every experiment. Thus, after Experiments Nos. 1 and 2 
had been carried out, which were merely preliminary so that I might learn something 
of the behaAuour of the apparatus, I arranged the balls in Experiment 3 as follows : — 

Lead ball, No. 1, Wall side, High level, 

„ 2, Arch „ Low ,, 
Gold „ „ 3, Wall „ High „ 

„ 4, Arch „ Low „ 
Neutral reading of lid 267°. 

The arch side is the right as seen from the telescope, or the left as seen from the 
back when the optical compass is in use. This expression depending upon the 
structure of the cellar avoids ambiguity. 

The corresponding arrangement in the whole series of experiments with the dates 
at which they were carried out is given in Table II. 

As would be expected, I had not at first all the details so complete as at the end 
of the series of experiments. Thus, in Experiment 3, the air drawing arrangement 
for steadying the mirror or starting it into motion, had not been thought of. At 
that time, for want of a better arrangement, I had to enter the corner and 
withdraw the back window, fig. 12, so as to allow the accidental movement of 
the air to start a swing of great amplitude. As I have already indicated, the 
decrement is, in spite of all I can do to prevent it, inconveniently high, so that 
periods extending over forty-five minutes cannot be taken unless the mirror has 
an oscillation of large amplitude at starting, far larger than two or three 
reversals of the lead balls in time with the oscillation would set up. The plan 
was essentially bad owing to temperature, disturbance, and tremor, nevertheless 
the observations made at the time were fairly consistent, thus two periods in 
the + position on October 16th, gave 24T93 and 241 - 90. The next day I put up 
the felt screens and two periods were 241"9(4) in the + position, and 24T88 in the 
negative. I then introduced a different method of producing a swing of great 
amplitude, viz., in the air tube then screwed into the back window, fig. 12, I fitted a 
glass stop-cock which could be turned on or off without touching the metal windows 
or screens. I did this hoping that a clockwork fan belongiug to a lamp would 
produce a gentle draught upon the end of the mirror when set in action opposite a 



NEWTONIAN CONSTANT OF GRAVITATION. 



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d 


d 


d 




<! 


£ 


£ 


fe; fc U5 


& 




fc 


is 


15 


!zi 


.of 

imont. 




















CO 


■* 


i« . CO i- 


CO 




OJ 


o 


F— ( 


CM 


o « 














r-H 


1— 1 


r-H 


* | 




















CD 





















MDCCCXCV. — A. 



K 



66 PROFESSOR C. V. BOYS ON THE 

funnel-shaped end to the pipe. This did not work, and I was therefore compelled at 
the time to produce the draught by some ready means ; gentle movement of a sheet 
of paper at a distance from the instrument produced the desired motion, but my 
going near the instrument at all was essentially bad. The periods obtained after 
this were : — 

Oct, 29. . . 241'99 + position. 

„ „ . . . 241-91 - „ 

„ 30 . . . 241-88 — 

„ „ . . . 241-93 + „ 

I noticed slight differences between periods taken with the lead balls in the + and 
— positions with my preliminary apparatus, but, though I am not able to explain it, 
I am glad to say that, with the more perfect setting and screening now in use, it has 
practically disappeared. The two periods taken with the counterweight gave identical 
results, 64 "9 5 4 seconds. 

The soldered fibres used in all the later experiments seem a definite improvement, 
as the creeping of the zero, which was never very troublesome, almost entirely ceased. 

The traffic and the trains are not the only causes of disturbance. "Wind, by 
pressing upon the building and neighbouring trees, of course shakes the ground ; but 
on Sept. 9-10, a particularly quiet night, I had to leave, owing to a sudden dis- 
turbance producing a pendular motion of 15 divisions, or 150 units, and for some time 
there was no quiet. As the motion was clearly produced by a lurch of the whole 
instrument and table carrying it, and was greater in amount than any traffic in the 
busiest part of the day had ever produced, and was moreover free from the high 
period tremor characteristic of human disturbance, I at once set it down to an earth- 
quake. I was marking transits of every 10 divisions at the time. The moment of 
the last mark was 15h. 44m. 14'3s., allowing for the error of the clock as determined 
at the Observatory. The next mark was due in 3 seconds, but I was, of course, 
unable to record it. In the 'Standard' of Sept. 12th there was an account of a 
violent earthquake at Jassy, which was felt also at Bucharest, at six o'clock in the 
morning. I have not ascertained the exact time at which the earthquake was felt in 
Ptoumania, or the amount to allow for difference of longitude, but these, no doubt, 
can be supplied from Vienna,* 

Experiment 11 was a purely comparative one. Everything being left as in Experi- 
ment 10, a tube was connected with the stop-cock in the bell-jar J, and with a 
hydrogen bottle and drying bottle, so that dry hydrogen could be fed in to displace 
the air in the central tube. The object was to see if any advantage would be derived 
from the smaller viscosity of hydrogen ; but, though the resistance fell so as to change 

* Mr. Charles Davison informs me that the shook was recorded at Bucharest at 3h. 40m. 35s., a.m., 
but that the epicentrum must have been some distance from there. The time interval between Bucharest 
and Oxford appears very small, the usual rate of travel being 3 km. a second, or a little more. 



NEWTONIAN CONSTANT OP GRAVITATION. 67 

the decrement from "842 to "937, which in itself was a great advantage, so much 
difficulty seemed inherent in the method that I determined not to prosecute it. The 
values found this night for T B 2 were 

In air 35404 

In hydrogen . . . 35401 

The deflections owing to disturbance could not be so accurately determined as usual ; 
they were 

In air 3520 

In hydrogen . . . 3523 

The only observation of real interest in connection with the hydrogen experiment 
was the effect of the gas upon the mirror. The mirror was bent to a small extent, 
causing the image of the divisions to practically disappear. A movement of the eye- 
piece outwards of about ■§ inch was needed to make them appear sharp again. On 
letting the gas escape the focus went back to its old place, and this was repeated 
without variation three or four times. I imagine that the glass became convex under 
the influence of the hydrogen in consequence of the glass being penetrated by the 
quickly-moving molecules, and so becoming expanded in the front or unprotected 
side, while the silver and lacquer at the back prevented this action, much as paper or 
lace will protect glass from the cutting action of a sand-blast. The bending may have 
been produced by a contraction of the lacquer or silver, but this seems hardly con- 
ceivable. An interesting line of inquiry is suggested by this experiment, but 1 have 
not been able to do more at present. 

An examination of the results shows that they hover about two values, experi- 
ments 3, 4, 5, 6 and 12 being about 5 "520 for A, and the remainder about 5 "528. It 
is impossible to trace any connection between the arrangement of the apparatus, &c, 
and this small irregularity. It is necessary, therefore, to review the deflections and 
periods of each and the conditions, whether of disturbance or quiet, under which they 
were carried out. No. 3 has already been discussed, and the wonder is that it should 
agree so well with the others when the imperfect conditions are borne in mind, and 
when it is remembered that the torsion fibre in this experiment had only one-third of 
the rigidity of those used later, while the gold balls were only half as heavy. 

As already mentioned, the periods in Experiment 4 were lost, so that an absolute 
result could not be calculated. The values of 2r in the two cases only differed by 
"00002 inch, an amount which is probably beyond the certainty of measurement, and 
therefore the results for 4 are merely obtained from those from Experiment 5, by 
multiplying or dividing by the ratio of the deflections. 

Deflections and periods for Experiment 4 were taken over several days. The 
deflections were : — 

K 2 



68 



PROFESSOR C. V. BOYS ON THE 



Temperature at "1 
end of night J 


Aug. 21. 


Aug. 23. 


Aug. 25. 


Aug. 26. 


Aug. 27. 


Aug. 29. 


36690 
3669-6 

17°-41 C. 


3667-7 
3668 
3666-7 
3667-8 

17°-04 C. 


3665-8 

(3664-9) 

3665-7 

16°-58 C. 


36697 
16°-56 C. 


3668-3 
16°-59 C. 


3668-3 
3669-0 
3669-4 

16°-24 C. 



The mean of all but the one in brackets, which depends on a single value only, is 
3668"1. The deflection for Experiment 5 is 3668"6, practically an identical quantity, 
so that the G and A of the two are almost the same. The two results should properly 
be considered as one. Both unfortunately depend upon unsatisfactory period obser- 
vations which, when squared, varied from 37200 to 37240. On this account the 
results from Experiments 4 and 5, which are higher than any of the others for G and 
lower for A, should have had a bad mark put against them. In Experiment 6 the 
deflections were nearly as consistent as those in Experiment 4, while the periods were 
now nearly the same in the + and — positions, being, when squared, 37245 in the — 
and 37247 in the + positions. The conditions of this experiment seemed decidedly 
favourable, and I see no reason inherent in the observations that could lead me to 
doubt the accuracy of the results. 

In Experiment 7 the only change was twisting the lead balls so that the sides that 
were inwards should be outwards. The sudden change in the result for A from 
5"5189 to 5"5291 might seem to be due to some irregularity of density in the lead 
balls. But the extraordinary agreement between this result and the three following, 
where every kind of change was made in the conditions, including the turning of the 
balls again, and the change from high to low and low to high, and where, moreover, 
the extra steadiness of temperature due to the screening of the octagon house was 
introduced, shows that this argument will not hold. 1 cannot account for this small 
difference. Iu Experiment 8 all the conditions were most perfect. The figures for 
this have already been given, and so need not be repeated. I may, however, compare 
the squares of the periods of Experiments 6, 7, and 8, throughout which the beam 
mirror and gold balls were never touched, to show how much better the agreement 
was at this time than before. 



Experiment. 


Date. 


— position. 


+ position. 


6 

7 
8 


Sept. 14 
„ 15 

., 17 


37245 


37247-5 

37242 

37245-9 



The last figure of this series was taken in determining S. I may mention that a 



NEWTONIAN CONSTANT OF GRAVITATION. 69 

change of -g 3 ^- inch, in 2R was made in this experiment, the effect of which is at once 
evident both in P the deflection, and in Q the geometrical factor. 

In Experiment 9, the conditions were completely changed by the substitution of 
gold cylinders for gold balls. As already mentioned, the torsional rigidity of the 
fibre was altered 5 per cent, by the great tensile strain, yet with eveiy quantity 
redetermined the only change in the result was about 1 part in 1500. The old 
conditions were realised again in Experiment 10, except that I had taken the fibre to 
London, re-soldered the broken ends and waited three months, but the result only 
differed from that of Experiment 8, by 1 part in 60,000. Perfect conditions were 
met with again, the mean deflections for the two nights, January 6 and January 7, 
being 3516'5 and 3516*3. The last experiment on January 21 was disturbed, and the 
points of rest varied several units in the course of the night. I was compelled, 
moreover, on leaving the apparatus at I7 h , to take off the gold balls, replace them 
by the counter-weights, and after about three hours' sleep, to return again and 
take the counter-weight period. This was far too soon for the temperature to have 
settled after disturbance, and in addition to this cause of error, I had only 10 minutes 
in which to take the period, and had then to hurry off with the drum record still wet, 
in order to be in London where I had to lecture at noon. I cannot, therefore, look 
upon this experiment with the same confidence as Nos. 7 and 10, and so with the 
exception of Experiment 6, all those that give the lower value for A have something 
against them. Under these circumstances, I cannot do otherwise than look to 
Experiments 7, 8, 9, and 10 as being the most likely to give a true value. Moreover, 
as Nos. 8 and 10 were both made under most favourable yet very different conditions, 
their closely agreeing figures carry more weight than the other two. I therefore 
conclude that A = 5*5270 and G = 6*6576 X 10 ~ 8 . The fifth figure in such case is, 
of course, a purely arithmetical phenomenon, but I do not think that the fourth 
figure can be more than 1, or at the outside 2 in error. 

I had hoped to have made a greater number of experiments under more widely 
differing conditions, but the strain which they entail is too severe, for not only have 
I had to give up holidays for the last three years, but to leave London on Saturdays 
and occasionally to sit up all Saturday and Sunday nights at the end of a week's 
work. The conditions, therefore, are too difficult for such an extended series as I 
should like to make to be possible, and I must after one more effort, leave the problem 
to others who have leisure, and what is of far greater consequence, a quiet country 
place undisturbed by road and railway traffic, and who possess the knowledge and 
manipulative skill which the experiment requires. 

Conclusion. 

I think it might be useful, now that the autumn has passed and I have been unable 
to make a new series of observations, if I were to state my views sa to any change of 



70 PROFESSOR C. V. BOYS ON THE 

detail that might conduce to greater accuracy. I am still convinced that G may be 
determined with an accuracy of 1 in 10,000 by means of apparatus such as I have 
described. 

In the general design I am unable to suggest any improvement. The weakest spot 
is caused by the resistance of the air making time work difficult, especially where 
visible shaking interferes with the usefulness of oscillations of small amplitude. I 
doubt if a practical gain is to be obtained by the use of hydrogen, and I am sure that 
a high vacuum is out of the question. The only remedy, therefore, is to employ 
larger suspended balls, and with them a longer beam. For the same argument that 
shows that with any length of beam the limit of sensibility imposed by the strength 
of the fibre is increased by reducing the weight of the suspended balls, for the rigidity 
of a fibre varies nearly as the square of its strength, shows also that if the fibres are 
not far from their breaking weight, the size of the balls cannot be increased without 
reducing the sensibility. But increase of size would be advantageous because, while 
the forces depend upon the cube of the diameter, the resistance to movement depends 
upon the square. The result is a less serious decrement with larger balls. Now, in 
order to employ these and yet maintain the period with the necessarily stronger 
fibre, a longer beam must be employed. Of course, unless the diameter of the large 
attracting balls are increased in the same proportion the angle of deflection will fall. 
I do not think that the beam needs to be lengthened to more than about two 
inches. If this length were adopted it would be better to aim at 5 centims., for since 
this is half a decimetre, a more accurate determination of the length could be obtained 
by reference to the standard decimetre at Sevres, than would be possible if it were not 
very nearly an exact submultiple. Whether or not the lead balls and the whole 
apparatus should be doubled in size is a mere question of cost. The expenses 
would run up very rapidly with very moderate increase of sensibility. I should feel 
disposed to be content with lead balls about six inches in diameter, but I would 
certainly have an Elmore tube for the centre one T, and, by preference, for the large 
cylinder C. The slight diminution of angular deflection which would result from this 
change, would be more than compensated by the doubled optical definition, but there 
might be some difficulty in obtaining a thin rectangular mirror 5X1 centims., in 
which no optical defect could be detected. 

It may appear that I am reversing all my arguments and practice in now advocating 
an increase of size, but it must be remembered that the object is not so much to 
increase the sensibility, or even to be able to make better geometrical determinations, 
for both of these, in my apparatus, exceed the square of the periods in the degree of 
accuracy with which they are known. The object is solely to be less influenced by 
the viscosity of the air, but this would not have limited the accuracy of my periods so 
seriously if I had not been disturbed by trains. 

I should have had less confidence in this doubling of the size, if my supposition 
that the disturbing moments, due to convection, were proportional to the seventh 



NEWTONIAN CONSTANT OF GRAVITATION. 71 

power of the linear dimensions, had been correct. Since it varies only as the fifth 
power, and the quietness of the air is so great in my apparatus (p. 11), there can be 
no objection on this account to the double size ; but I would strongly urge that in 
such a case, a room more uniform in temperature than the one at Oxford should be 
employed. It would also be well to lay non-connecting mats on those parts of instru- 
ments on which the hands are apt to rest when the balls are being transferred, or 
other manipulative operations are being carried out, so as to reduce, as far as possible, 
access of heat, and hence the interval that must elapse before observations of 
deflections or periods can be undertaken. I do not think any ready-made room is 
likely to be found available. A disused adit, at a great distance from existent 
mining operations, would be perfect, if it could be made use of. The instrument 
could then be walled up in a room to itself, and the heat from the observer and the 
travelling lamp excluded far more perfectly than in my case. An adit would be 
convenient also, in that it would allow of the use of a greater distance from the scale 
to the mirror than could be obtained in an ordinary room. This should not be less 
than 20 metres. 

I should recommend a slight change in the upper end of the lid pillars with the 
object of giving the bail holder two adjustments, one radially, and one at right angles 
to a radius, so that eccentricities observed by the microscope of the optical compass 
could be corrected. 

I also think more pains should be taken with the beam mirror to insure its rotating 
about its own centre of gravity, both when the gold balls and when the counter- 
weight are suspended. This would remove any doubt as to its constancy of move- 
ment of inertia when made to oscillate under the three conditions, and would at the 
same time make observable eccentricity of the gold balls impossible. 

Finally, I have suffered much from the great loss of time that results from the 
accidental fall of a gold ball down the central tube. It can only be replaced after 
lifting out the torsion head, torsion fibre, and beam mirror, so that all the centering 
adjustments are lost, besides which, there is the serious risk of breaking the torsion 
fibre whenever this operation is carried out. I would make the lower end of the 
central tube funnel-shaped inside, and employ a much larger holding down screw, 
with a central hole more than large enough to allow the gold ball to escape through 
it. This could, of course, be plugged at other times. In order to put the gold balls 
into their places without removing the torsion fibre, I would have a large hole in the 
torsion head behind (away from the big telescope) the torsion rod, and this would be easy 
with the larger central tube. Then if a special overhead wheel were placed with its 
edge vertically over the centre of this hole, the gold ball could be let down as 
described in the paper and transferred, as usual, on to one of the side hooks by the 
use of a simple tool made of a bent pin. 

In every other respect the apparatus behaves so perfectly, and the operations are 
conducted with such facility, that I am unable to offer any other useful suggestion. 



72 



ON THE NEWTONIAN CONSTANT OF GRAVITATION. 



Description of Plates 1 and 2. 



PLATE 1. 



Fig. 1 is a vertical section, and fig. 2 a sectional plan of tlie apparatus. Fig. 3 is a front view of a 
portion of it. Figs. 4, 5, 6 show details of the lid, pillars, and ball-holders on a larger scale. Fig. 7 
represents the beam-mirror, counterweight, and eye-hooks full size. Figs. 8 to 10 show the window 
apertures in the central tube, beam raiser, &c, on a larger scale. Figs. 11 and 12 are the front and 
back windows used when deflections and periods are being observed. Figs. 13 and 14 show the back 
window for use with the optical compass. Fig. 15 represents the tubular screens; figs. 16 and 17, the 
mould for pressing the 4^-inch lead balls. 

PLATE 2. 

Figs. 18, 19, 20, and 21 are plan, side, and end elevations of the cellar with the apparatus in position. 
Fig. 22 is a horizontal section of the octagon house, the position of the apparatus being shown in dotted 
lines. Fig. 23 is an isometric projection of the geometrical clamps holdiug the scale and dummy. 
Figs. 24, 25, 26 are plan, front and side views, of the rotating and focussing slides and scale of the 
optical compass in position on the lid of the instrument, which is represented in chain lines. Figs. 27, 
28, 29 are plan, front and side views, of the traversing slides and microscopes of the optical compass in 
position on the focussing slide, which is represented in chain lines. 

Scale of Figs. Plates 1 and 2. 



Scale .... 


1 

4 


1 
3 


i 

2 


1 


J inch to foot. 


Figure . . . 


15 


1 


4 


7 


18 




16 


2 


5 




19 




17 


3 


6 




20 




22 


24 


8 




21 




23 


25 
26 
27 
28 
29 


9 
10 
11 
12 
13 
. 14 







Boys. 



Phil. Trans. 1895 .A . Plate 1 . 





" r~ 


\ 




® 


:vro 


1 


@=* i 1 


u. 




Tfcst.N™™"" I" 



PhiL.Trarus. 1895. A . Plate. 2. 




• 'Z V;l 



Phi/. Trans. 1895. A . PUu 2. 




[ 73 ] 



II. On the Photographic Spectrum of the Great Nebula in Orion. 
By J. Norman Lockyer, C.B., F.R.S. 

Received June 13, — Read June 21, 1894. 

Contents. 

PAGE. 

I. Description of the photographs 73 

II. Table of wave-lengths 76 

III. The origins of the lines recorded 77 

IV. The variation of the spectrum in different regions of the nebula 78 

V. Discussion of the results in relation to the meteoritic hypothesis 81 

(a) The complex origin of the spectra of nebulte ■. . 82 

(o) The passage to bright-line stars 82 

(c) Relation to stars of Groups II. and III 85 

VI. General conclusions 91 

I. Description oe the Photographs. 

In February, 1890, I communicated to the Royal Society a preliminary note on some 
photographs of the spectrum of the Orion Nebula, taken at West-gate- on- Sea.* 

The detailed discussion of the photographs has been reserved with the hope of 
securing others, but owing to other pressing work no further photographs have been 
obtained. 

As the photographs in question show a greater number of lines than others which 
have been described, and especially as they appear to have an important bearing on 
the study of certain types of stellar spectra, I have thought it desirable that the 
publication of the results should no longer be delayed. 

The instrument employed was the thirty-inch reflector, and a spectroscope by 
HlLGER, having one prism of 60° and two half-prisms of 30°. 

Mawson's instantaneous plates were used. The exposures were carried up to four 
hours, and five photographs were taken, some of them with shorter exposures than 
that named, in consequence of the sky becoming clouded or irregularities in the driving 

* 'Roy. Soc. Proc.,' vol. 48, p. 199. 
MDCCCXCV. — A, L 5 3.95 



74 



PROFESSOR J. N. LOCKYER ON THE PHOTOGRAPHIC 



clock, which was not then completely finished. One plate was exposed for four hours, 
on February 11, 1890, but, unfortunately, in consequence of the high wind, the slit 
was covered for an unknown part of this time by the velvet used to keep out stray 
light, and this was not at once discovered, as the finder for directing the telescope is 
at the lower end of the reflector tube, away from the spectroscope. This photograph 
only shows three or four of the more prominent lines, but they are all sharply defined. 
The other photographs were taken on February 2, 8, 9, and 10, the last with an 
exposure of three hours. 

As a collimator has not yet been fitted to the tube of the reflector, the exposure of 
the plate to the flame of burning magnesium was made by closing the mirror cover, 
and burning magnesium at its exact centre. One half of the slit was exposed to the 
nebula, and the other half to the burning magnesium. 

The part of the nebula photographed was the bright portion in the region of the 
trapezium. In some photographs, in consequence of clock irregularities, the stars 
of the trapezium have imprinted their spectra upon the plates, but these in no way 
interfere with the spectrum of the nebula, since a longish slit was used, and the 
spectra of the stars are narrow. 

There is a remarkable and almost absolute similarity between the photographs 
obtained. The best one, taken on February 10, shows all the lines of the other 
photographs with ethers in addition, and this has therefore been selected for the 
determination of wave-lengths. 

The probable mean position of the slit during the three hours' exposure of this 
photograph is shown in fig. 1, but the irregularities in the driving caused all the 
stars in the trapezium to cross the slit at different times. 




Fig. 1. Skewing mean position of slit in photograph of February 10, 1890. 



It has not been found possible to reproduce the negative with advantage in 
consequence of its small size, but fig. 3 (see p. 80) gives a good idea of the appearance 
of the eleven principal lines shown in the photograph, and the position of the stellar 
spectra on the plate. Further reference to this diagram will be made later. 

The principal lines are the three ordinarily seen in the visible spectrum, the lines of 



SPECTRUM OF THE GREAT NEBULA IN ORION. 75 

hydrogen at H v , H 5 , H e) and H f , and the strong line in the ultra-violet near X373. 
H y is by far the strongest line in the spectrum. The wave-length of the least 
refrangible line on the photograph was taken as 5006 - 5, as determined at Ken- 
sington, and this, together with the hydrogen lines, the line at X4471, and the 
ultra-violet magnesium triplet in the comparison spectrum, formed the basis of the 
curve for determining the positions of the fainter lines. The photograph was 
measured with a micrometer reading to 0"00001 inch. 

All the lines are shown in the table which follows. In all, fifty-four lines have 
been recorded, and, of these, about twenty are seen without difficulty. The remainder 
require a favourable light, but no line has been inserted in the table which has not 
been measured several times by two observers. The spectrum extends from the 
ultra-violet to the green, and the intensities of the lines on the photographs 
naturally do not correspond to the visual ones ; the F line, for instance, appears 
stronger than the brightest line in the visible spectrum at X 5006. The photographic 
intensities are recorded in the table, six representing the strongest and one the 
feeblest line. 

Some of the wave-lengths referred to in the preliminary paper have been slightly 
changed by the new reduction. 



L 2 



76 PROFESSOR J. N. LOCKYER ON THE PHOTOGRAPHIC 

II. Table of Wave-lengths. 
Table I. — Lines Photographed in the Spectrum of the Orion Nebula, Feb. 10, 1890. 



Micrometer 


"Wave- 


Photographic 


Probable 


Wave-length of pro- 


Remarks. 


reading. 


length. 


intensity. 


origins. 


bable origins. 


3-3(572 


3707 


2 








3 3632 


3715 


1 








3-3565 


3729 


6 








3-3455 


3743 


1 








3-3410 


3752 


1 


H 


3749-8 


H c 


3-3310 


3770 


1 


H 


3769-4 


H t 


3-3200 


3796 


2 


H 


3796-9 


He 


3-3020 


3832 


2 


H 


38345 


H, 


3-2950 


3S47 


1 








3-2910 


3855 


1 








3-2850 


3868 


4 








3-2762 


3887 


4 


H 


3887-8 


H f 


3-2690 


3902 


2 








32656 


3910 


1 








3-2565 


3933 


2 


Ca 


3933 


K line, Solar Spect. 


3-25-25 


3941 


1 








3-2+95 


3949 


1 








3-2415 


3968 


5 


Ca H 


3968 


H e 


32356 


3984 


1 








32295 


4000 


3 








3-2251 


4010 


2 




. 




32197 


4025 


3 








32136 


4041 


1 








3-2"85 


4054 


2 








3-2035 


4067 


2 








3-1969 


4086 


1 








3-1915 


4101 


6 


H 


4101 


H« 


3-1819 


4120 


1 








3-1818 


4129 


1 








31771 


4142 


1 








3-1722 


4154 











3-1682 


4167 


1 








3-1560 


4204 


1 








31491 


4226 


1 


Ca 


4226 


Flame line 


3-1464 


4234 


J. 








3-1360 


4269 


2 








3-1160 


4340 


6 


H 


4340 


H y 


31030 


43S5 


1 


Fe 


4383 


Strongest flame liue of 


3-1020 


4389 


2 






iron 


30972 


4410 


1 








3-0929 


4426 


2 








3-0810 


4471 


4 






LOREXZONl'S /. 


3-0750 


4495 


3 








30645 


4539 


2 








3-0450 


4627 


2 








3-0275 


4715 


2 








3-0230 


4735 


1 


C 


4736 




3-0070 


4S24 


3 








3-0040 


4839 


2 








3-0000 


4861 


6 


H 


4861. 


H? 


2-9935 


4897 


3 








2-9892 


4923 


3 








2-9S35 


4957 


4 








2-9750 


5006-5 


5 


Mg 


£006-5 


" Chief " line 



SPECTRUM OF THE GREAT NEBULA IN ORION. 77 

III. The Origins of the Lines. 

It will be seen from the table, that hydrogen enters largely into the composition of 
the vapours of the nebula. ELj H y , H s , H £ , and the ultra-violet series, certainly as far 
as H„. (new notation),* are all present. 

It is worthy of remark, however, that while, as previously stated, H y is the strongest 
line in the whole spectrum, and H^, H s , and H e are also strong, the ultra-violet 
hydrogen lines are amongst the weakest. 

Next to H v , the line A 373 is the most intense. In 1887, I suggested that this line 
was one of the members of the triplet seen in the spectrum of burning magnesium. 
As I stated in a preliminary communication, the wave-length could not be finally 
determined from the photographs already obtained, but it was probably near A 3729. 

This value, however, will require correction for motion in the line of sight. If Mr. 
Keeper's valuest for the motion be accepted, and the earth's orbital velocity be 
allowed for, the correction will be about - 22 tenth metres towards the red. This will 
bring the nebular line slightly nearer the least refrangible member of the magnesium 
triplet. Further measures of photographs taken with higher dispersion are necessary 
in order to settle this point. 

The lines next in importance to those already mentioned, are near wave-lengths 
4471, 4495 and 3868. The first of these, the strongest between H 3 and H,,, is 
probably the line observed by Dr. Copeland in 1886. With reference to this line, 
I wrote as follows in a paper communicated to the Royal Society on Nov. 9, 1889.J 

" The observations of Dr. Copeland have now, I think, established the identity of 
the yellow line, in the nebula of Orion at all events with D 3 . In a letter to 
Dr. Copeland, I suggested that the line at A 447 was, in all probability, Lorenzoni's 
f of the chromosphere spectrum, seeing that it was associated both in the nebula and 
chromosphere with hydrogen and D 3 . This he believes to be very probable. The line 
makes its appearance in the chromosphere spectrum about 75 times to 100 appearances 
of D 3 , or the lines of hydrogen." 

For the other strong lines near A 3868 and A 4495, no origins have been found. 

From the final reduction of the photographs, as given in the table, it appears that 
the fine formerly said§ to be "near A 4027," is at X 4025. It can, therefore, no 
longer be attributed to manganese. Its origin is at present unknown, but, as will 
appear later, it is a line frequently met with in the spectra of other celestial bodies. 
The line at X 4690 referred to above, does not appear in the revised list, which only 
contains lines measured without great difficulty. Further, only a small proportion of 
the fines now mapped can be ascribed to metallic origins, but these, it will be seen, are 

* Vogel, ' Ast. Nach.,' 3198, 1893. 

t 'Roy. Soc. Proc.,' vol. 49, p. 400, 1891. 

t Ibid., vol. 47, p. 30. 

§ Ibid., vol. 48, p. 200. 



78 PROFESSOR J. N. LOCKYER ON THE PHOTOGRAPHIC 

the chief lines in the spectra of the elements concerned. The table shows that a large 
number of the lines appear to have no terrestrial equivalent, but they are present in the 
spectra of other celestial bodies. These coincidences are discussed in a subsequent part 
of the paper. 

IV. The Variation of the Spectrum in Different Regions of the Nebula. 

The earlier investigations of the photographic spectrum of the Orion Nebula 
seemed to indicate that the spectrum was different for different regions. 

In my own observations in 1891, with the 30-inch reflector at Westgate, the 
variations were very striking. 

I stated in a paper communicated to the Royal Society in December, 1889,* "I 
obtained momentary glimpses of many bright lines between ELj and H y , on October 31." 
These were also seen by Mr. Fowler, and it was observed that, as the nebula was 
swept across the slit, in some parts the lines were seen together, while in other parts 
first one group and then another made their appearance. In the same paper I 
referred also to the variations in the same field of view of some of the lines. These 
observations were made with an enlarged form of pocket spectroscope, with a 
dispersion that does not split D. I found that in certain parts of the nebula, in the 
same field, certain lines were knotted, as often seen in prominences on and off the sun, 
and in other parts broken ; in the former case, whilst the F line thickened equally on 
both sides, the chief nebular line thickened only on the more refrangible side.t 

This result is shown in fig. 2. 

* ' Roy. Soc. Proc.,' vol. 48, p. 195. 

f In another paper ('Phil. Trans., 'A, 1893, vol. 184, p. V14), I wrote as follows with regard to the 
chief line : " I have convinced myself of the fluted nature of the line by new observations made with 
instruments best fitted to show it, while the Lick telescope is, perhaps, the ideal telescope not to employ 
in such an inquiry. Hence, although the visibility of magnesium is not fundamental for my argument, 
I still hold that it is more probably the origin of the nebular line than an unknown form of nitrogen." 
The recent remarks of Professor Keeler (' Ast. and Ast. Phys.,' January, 1894, p. 61), and Mr. 
Campbell (' Ast. and Ast. Phys.,' May, 1894, p. 385), as to the relative efficiency of telescopes in regard 
to the observation of spectrum lines, seem to indicate that the matter has not been sufficiently thought 
out. I have not seen a statement as to the percentage of light utilised in the case of the Lick telescope, 
but I may say that at the time my observations were made, the mirrors of my telescope were newly- 
silvered, so that probably only a small percentage of light was lost. Neglecting the loss of light due to 
absorption in the case of the refractor, and to reflection in the case of the reflector, the brightness of the 
image formed on the slit of the spectroscope by the Westgate telescope is about sixteen times that of 
the image formed by the Lick telescope, and it is scarcely necessary to add that having this great 
illuminating power, the collimator of the spectroscope has been designed to take full advantage of it. 
[Professor Campbell, who has succeeded Professor Keeler at the Lick Observatory, is of the same 
opinion as myself. He writes ('Astr. and Ast.-Phys.,' 1893, p. 53) : "The 36-inch telescope presents 

several positive disadvantages The ratio of the focal length 19 : 1 is much larger than 

exists in small telescopes, and hence the latter would form much brighter images on the slit plate." 
Note added 4.1.95.] 



SPECTRUM OF THE GREAT NEBULA IN ORION. 79 

This was confirmed by Messrs. Fowler and Baxandall at Kensington, with the 
10-inch equatorial, on October 31 and November 1, and again by Mr. Fowler with 
the 30-inch on November 2. 




Fig. 2. Difference in the appearance of the lines at 4862 (P) and 5006'5. 

It is also recorded in the Observatory note-book that at times these lines appeared 
of unequal length, the spectroscope employed in the observations having a long slit, 
and that sometimes 500 and 495 were seen without H^. In the photographic 
investigation of variations in the spectrum, the question is complicated by differences 
in sensitive films, and in the case of a silver- on -glass reflector by the conditions of 
the mirrors. My own experience has shown that when mirrors are tarnished, the 
ultra-violet portion of the spectrum is weakened in greater proportion than the violet 
and blue. 

One of the most striking variations previously recorded is that of the strong line 
in the ultra-violet near X 373. This was the strongest line in the photograph taken 
by Dr. Huggins in March, 1882,""* but it was not shown in Dr. Draper's photograph 
taken in the same year.t 

Dr. Draper says : " I have not found the line at 3730, of which he (Dr. Huggins) 
speaks, though I have other lines which he does not appear to have photographed. 
This may be due to the fact that he had placed his slit on a different region of the 
nebula, or to his employment of a reflector and Iceland spar prism, or to the use of a 
different sensitive preparation. Nevertheless, my reference spectrum extends beyond 
the region in question." 

A later photograph (1889), taken by Dr. Huggins,"}; did not show the line in 
question, the slit being placed on a different part of the nebula. As already stated, 
the line is one of the strongest in my photographs, though it is not quite as strong as 
Hy. The spectrum photographed by Dr. Huggins, in 1889, differed entirely from 
those photographed by him in 1882 and 1888, the slit being again placed on a 
different region of the nebula. 

My own photographs are specially interesting, as they indicate differences even in 
the small area of the nebula which is covered by the slit during a single exposure. 

* ' Roy. Soc. Proc.,' vol. 33, p. 427. 

t ' Amer. Journ. of Science,' vol. 23, p. 339. 

X 'Roy. Soc. Proc.,' vol. 46, p. 41. 



80 



PROFESSOR J. K LOCKYER ON THE PHOTOGRAPHIC 



Some of the more important variations are indicated in fig. 3. The stars, the spectra 
of which are registered on the plate, will be readily identified by a comparison of 
figs. 1 and 3, the spectra of the trapezium stars being shown at the bottom of the 
diagram, and that of the star G. P. Bond 685 (Herschel's e) at the top. 

It will be seen, for example, that the line near X 495 falls off in intensity about 
the middle of its length, while the lines of hydrogen show no such reduction in the 
same part of the nebula. If we first consider the phenomena, in the neighbourhood 
of the star G. P. Bond 685 (Herschel's e), near the trapezium, it will be seen 
that here the lines 4471 and 4495 are most intense. In this region there is also a 
distortion of the two lines at 4471 and 4495 ; they are sharply bent towards the 
red end of the spectrum, whilst the other lines remain straight. Unfortunately, the 
spectrum of this star is only shown on the photograph of February 10, and, in the 
absence of other photographs, it is possible that the displacement of the two lines in 
question may be due to a distortion of the gelatine film. The displacement of the 
lines, if real, would indicate a velocity of about 200 miles per second, in the line of 
sight. Both lines are brightest where they are most disturbed. 




Fig. '6. Diagram showing the principal lines in the photograph of the spectrum of the Orion nebula, 
February 10, 1890, with their relative intensities. The spectra of the stars in the trapezium are 
shown at the bottom of the diagram, while that at the top is the spectrum of the star Bond 685. 



It will be seen, also, that where the lines of the nebula cross the continuous 
spectrum of the star, they are considerably broadened. This is seen in all the 
principal lines from X 373 to X 495. 

Where the chief line (500) crosses the spectrum of the star, there is a decided 
indication of a reversal. As it approaches the star, the line bifurcates and reunites 
on the other side, leaving a short dark line where it crosses the spectrum of the star, 
as shown in fig. 3. This reversal is not seen in the case of the hydrogen lines, but if 
it be subsequently confirmed in the case of 500, it will be an indication that some of 
the nebulous matter lies in front of the star in question (Bond 685 ; Herschel e). 



SPECTRUM OP THE GREAT NEBULA IN ORION. 81 

Coming now to the region of the nebula about the stars of the trapezium, it will be 
seen from fig. 3 that the bright lines are considerably widened where they intersect 
the spectra of the trapezium stars. In this case the hydrogen line at X 4340 is 
widened very little on the less refrangible side, while, on the more refrangible side, 
the widening is nearly as great as its own breadth. Further, on each side of the line 
there is a decided break in the continuous spectrum of the stars, giving the appearance 
of a broad absorption band, with the bright hydrogen line running through it. This 
appearance is almost exactly reproduced at H s . 

Dr. Draper* appears to have noticed a peculiarity in the hydrogen lines where 
they crossed the spectra of the trapezium stars in his photographs of 1882. He says : — 

" The hydrogen line near G, wave-length 4340, is strong and sharply defined ; that 
at h, wave-length, 4101, is more delicate ; and there are faint traces of other lines in 
the violet. Among these lines there is one point of difference, especially well shown 
in a photograph where the slit was placed in a north and south direction across the 
trapezium ; the H line, X 4340, is of the same length as the slit, and, where it 
intersects the spectrum of the trapezium stars, a duplication of effect is noticed. If 
this is not due to flickering motion in the atmosphere, it would indicate that 
hydrogen gas was present even between the eye and the trapezium. 

" I think the same is true of the H 8 line, X 4101." 

The line at 500 is only feebly impressed in the neighbourhood of the trapezium 
stars, and no reversal is visible. 

It is clear, therefore, that the spectrum of the nebula varies very considerably in 
different regions. 



"E> 



V. Discussion of Results in Relation to the Meteoritic Hypothesis. 

In my paper, " On the Photographic Spectra of some of the Brighter Stars," com- 
municated to the Royal Society in November, 1892,t I made reference to the spectra 
of nebulas in relation to the meteoritic hypothesis. The statements were based upon 
an incomplete reduction of the photographs of the spectrum of the Orion nebula, and 
I now proceed to show how the hypothesis bears the test when the final reductions 
are considered. 

On the hypothesis : — 

(a) The normal spectrum of the nebulas, including planetary nebulae!, should have 
a complex origin. 

(b) The bright-line stars are simply nebulas further condensed. 

(c) "With further condensation a group of stars of increasing temperature, with 
spectra consisting of mixed bright and dark fiutings, is produced. 

(d) Still further condensation results in a group of stars of increasing temperature, 
with spectra of dark lines, differing from the solar spectrum. 

* ' Amer. Journ. of Sci.' (3), vol. 23, p. 339, 1882. 
t ' Phil. Trans.,' A, 1893, vol. 184, p. 713. 
MDCCCXCV. — A, M 



82 PROFESSOR J. N. LOCKTER ON THE PHOTOGRAPHIC 

(a) The Complex Origin of the Spectra of the Nehulce. 

As pointed out in the paper referred to, the bright lines should have three origins, 
namely : — 

(1) Non-condensable gases driven out of the meteorites. 

(2) Low tempei'ature vapours produced by a large number of feeble collisions. 

(3) High temperature vapoui'S produced by a small number of end-on collisions. 

It will be seen from the tables that the requirements of the hypothesis in this 
respect are fully satisfied. 

The lines of hydrogen and the flutings of carbon are what we should expect from 
the large interspaces ; the flutings of magnesium and the low temperature lines of 
iron and calcium bring us face to face with phenomena connected with low tempera- 
tures, and they may be ascribed to the partial collisions ; while the lines coincident 
with chromospheric lines must be regarded as high temperature products, since the 
solar chromosphere may be taken as indicating the spectrum we might expect to be 
associated with the high temperature vapours produced by the end-on collisions. 

The undoubted presence of the lines D 3 and X4471 left but little doubt as to the 
chromospheric relationship of some of the lines in the nebular spectrum, but the. flood 
of new light thrown by the photographs taken with the prismatic cameras during the 
total eclipse of the sun on April 16th, 1893, put the matter beyond all question. 

The discussion of the eclipse photographs will form the subject of a separate 
communication, but it may be here stated that the spectrum of the nebula shows a 
number of coincidences with lines seen in the spectrum of the chromosphere and 
prominences. 

(b) TJie Passage to the Bright-Line Stars. 

The association of the nebulas with the bright-line stars in the classification of the 
heavenly bodies was, I think, first suggested by me in 1887.* 

So far as the planetary nebulae are concerned, this grouping has been abundantly 
confirmed by Professor Pickering's work on the bright-line stars, and by the visual 
observations of Professor Keeler. 

Professor Pickering! tabulates the lines, and concludes with the statement that, 
" Owing to the similarity of the spectra of the planetary nebulae and the bright-line 
stars, they may be conveniently united in a fifth type." It is clear then, that in this 
particular, Professor Pickering accepts my proposed classification. 

Mr. Keeler writes,} " The spectra of the nuclei of the planetary nebulas have a 
remarkable resemblance to the Wolf-Rayet and other bright-line stars, and an 

* ' Roy. Soc. Proc.,' vol. 43, p. 144. 

t 'Ast. Nack,' 3025, 1891. 

X ' Proc. Ast. Soc. Pacific,' vol. 2, No. 11, Nov. 29, 1890. 



SPECTRUM OP THE GREAT NEBULA IN ORION. 



83 



intimate connection between these objects, if established by further observations, 
would place the bright-line stars first in the order of development. The D 3 line 
appears in the central condensation of a number of bright nebula?, and with sufficient 
light would probably be seen in many of them, and this line is also predominant in 
most of the bright-line stars." 

One of the main points of this paper is to show that the relationship indicated 
between the planetary nebulae and bright-line stars also holds good for such a nebula 
as that of Orion. 

The bright lines seen in the visual spectra of the two classes of nebulae have long- 
been known to be identical, and a comparison of the Westgate photographs with the 
results obtained by Professor Pickering, and the more recent work of Gothard,* and 
of Professor Campbell, at the Lick Observatory, on the spectra of the planetary 
nebulae,t has shown that the similarity also extends to the photographic region. 

The fact that some of the nebular lines were apparently coincident with lines in the 
bright-line stars, was recognized at an early stage in the reduction of the Westgate 
photographs, and in the preliminary note I wrote as follows : " It is a very striking 
fact that some of the chief lines are apparently coincident, although the statement 
is made with reserve, with the chief bright lines in P Cygni, a magnificent photo- 
graph of which I owe to the kindness of Professor Pickering ; it is one of the 
Henry Draper Memorial photographs." 

The bright lines here referred to were those of hydrogen, and lines at 4025 and 
4471. All these have since been photographed at Kensington, in the spectrum of 
P Cygni, and there is no longer any doubt as to their identity with bright lines in 
the nebula. Additional bright lines in the spectrum of P Cygni, photographed at 
Kensington, are also seen in the nebula, as shown in the following table : — 

Table II. — Comparison of Orion Nebula with P Cygni. 



Orion nebula. 


P Cygni (Kensington). 


39G8 


3968 H e 




4015 


4025 


4025 




4035 


4101 


4101 H 5 




4147 


4340 


4340 H Y 


4471 


4471 


4715 


4715 




4840 


4=61 


4861 Hp 


4923 


4923 



* 'Astr. and Ast.-Phys.,' 1893, p. 51. 
t Ibid., p. 276. 

M 2 



84 



PROFESSOR J. N. LOCKTER ON THE PHOTOGRAPHIC 



Table III. shows in a complete form the details of the coincidences of the lines in 
the spectrum of the Westgate photograph of the Orion nebula with those of 
planetary nebulae and bright-line stars, as given by Pickering and Campbell. 
Only those lines of the nebula which show coincidences are included in this table, 
but the spectra of the planetary nebulae and bright-line stars are tabulated in full.* 

It will be seen that all the lines of the planetary nebulae, photograj)hed by 
Pickering, appear in the Orion nebula, while of the twenty lines photographed by 
Campbell, twelve are present. Of fifteen lines in the spectra of the bright-line 
stars, eleven appear in the nebula. 

Table III.— Comparison of Orion Nebula with Planetary Nebulae and Bright-line 

Stars. 





Planetary nebula?. 


Planetary 


Bright-line 


Bright-line 


Bright-line 


Orion nebula. 


(Campbell.) 


nebuhe. 


stars, Type I. 


stars, Type II. 


stars, Type III. 




(Rowland's Scale.) 


(Pickering.) 


(Pickering.) 


(Pickering.) 


(Pickering.) 


386S (4) 


3867-8 










3887 (4) 


3888 


388 


389 


389 




3949 (1) 


. , 


. . 


395 


, . 


395 


3968 (5) 


3969 


397 


39S 


397 




4025 (3) 


4026 


, , 


402 


402 




4067 (2) 


4067 


. . 


406 


406 


407 


4101 (6) 


4102 


410 


410 


410 




4120 (1) 


. , 


. , 


. , 


. . 


412 


4204 (1) 


, . 


. . 


420 


420 


421 


4340 (6) 


4341 


434 


434 


434 


434 


, . 


4363-4 










4389 (2) 


4390 










4426 (2) 


, . 


, . 


, . 


. . 


443 


4471 (4) 


4472-3 


447 


, , 


447 




, . 


. t 


. . 




451 


451 


. , 


, . 


, . 


454 


455 


455 




4574 










t . 


4595 










. . 


4610 










. , 


4631-40 


. , 


462 


464 


464 


. , 


4663 










, . 


4686-8 


, , 


469 


469 




4715 (2) 


4714-6 

4743 


470 








4861 ' (6) 


4862 


4S6 


486 


486 




4957 (4) 


4958 










5006-5 (5) 


5007 


501 









* Professor Pickering has been good enough to furnish me with glass copies of his beautiful photo- 
graphs of the spectra of some of the bright-line stars. The positions of the various lines which he 
gives are in the main confirmed by the new measures -which have been made at Kensington. I am in 
communication -with him as to additional lines which have been mapped. 

[In conseqitence of the delay in printing this paper, I am enabled to state that Professor Campbell has 
communicated some most important observations to ' Astr. and Ast.-Phys.,' 1894, p. 448, on the Wolf- 
Ratet stars, which show that the number of coincidences with lines in the nebula of Orion and planetary 
nebulae is increasad by 7, — Note added 4.1.95.] 



SPECTRUM OF THE GREAT NEBULA IN ORION. 85 

(c) Relation to Stars of Groups II. and III. 

With further condensation, the interspaces between the meteorites will be reduced, 
and the bright -line stars will pass to stars with absorption spectra in which the dark 
lines correspond with the bright lines of the nebulae. There will, however, be inter- 
mediate stages (Group II. and the early stages of Group III.), as I have already 
pointed out.* At these stages, some of the high -temperature lines do not appear 
either as bright or dark lines, and this, no doubt, for the reason that the radiation 
from the interspaces is masked by the absorption of the vapours in the immediate 
neighbourhood of the meteoritic stones. In these stars the hydrogen lines are 
normally feeble dark lines, but the amount of radiating area in a cross section is so 
nearly ecpial to the amount of absorbing area that disturbances which, according to 
the meteoritic hypothesis, produce the increase of light in the variable stars of the 
group, are sufficient to make the hydrogen lines appear bright. 

When we pass to the more condensed bodies, we find a group of stars, of which 
y Cygni is a typical case, in which the dark lines are very numerous,t but different 
from those which appear in the solar spectrum. This difference, however, is not 
taken account of in Vogel's classification of stellar spectra. It may be added that 
photographs of the spectra of other stars resembling y Cygni have been obtained since 
the date of the paper referred to. 

At a still further stage of condensation we get stars in which there are only a 
relatively small number of lines, and these are lines which appear in the nebulas. 
This similarity became evident at an early stage of the discussion of the photographic 
spectrum of the Orion nebula, and a comparison with the spectrum of a. Andromeda? 
was given in the paper communicated to the Royal Society, in November, 1892.J 

The first suggestion of such a relation appears to have been made by Dr. Scheiner, 
of Potsdam,§ who pointed out that the strong line at X 4471, which had been observed 
in the Orion nebula by Dr. Copelakd, was also seen in the Potsdam photographs of 
the spectrum of Rigel. This line is one of the brightest in the nebula photographs 
now under discussion, and is seen in the spectra of a large number of stars of the type 
of Eigel and Bellatrix. 

The spectra of such stars in the region between K and X 472 are described in my 
paper referred to above ; and in Table IV. they are compared with the spectrum of 
the Orion nebula. It will be seen that out of 31 lines in the nebula in the region 
compared, 20 are coincident with stellar lines. || 

* ' Phil. Trans.,' A, 1893, vol. 184, p. 711. t Ibid., p. 698. J Ibid., p. 719. 

§ 'Ast. Nacb.,' 2923, p. 328, 1889. 

|| It may be added that D 3 , which appears bright in the nebula, was observed by Mr. Fowler as a 
dark line in the spectrum of -/ and 'C, Orionis, on Dec. 12, 1893, and in Rigel on March 4, 1894. It does 
not, however, appear in the spectrum of Sirius or a. Lyras. D 3 has also been photographed as a dark line 
in the spectra of /3 and o Orionis, by Mr. Campbell at the Lick Observatory. ' Astr. and Ast. Phys.,' May, 
1894 p. 395. 



86 



PROFESSOR J. N. LOCKYER ON THE PHOTOGRAPHIC 



Table IV. — Comparison of Orion Nebula with Stars of Groups II. and III. 

(Region K to \ 472 Angstixim). 















Group 


IILy. 






Orion nebula. 


Group II. 


Group Ilia. 






































"Cyg 


ni. 


Rigel. 


Bellatrix. 


S Orionis. 


a. Virginia. 


K 3933 (2) 


3933-6 


3933-6 


3933 


(6) 


3933 (6) 


3933 


(3) 


3933 


(1) 


3933 (1) 


3941 (1) 






















3949 (1) 






















. , 




, . 


3961 


(6) 














. , 


. . 


- . 






3963 (2) 


3963 


(3) 


3963 


(2) 




(He) 3968 (5) 


3968 


3968 


3968 


(6) 


3968 (6) 


3968 


(6) 


3968 


(6) 


3968 (6) 


3984 






















, . 


. . 


» , 


. , 




3994 (1) 


3994 


(3) 


3994 


(2) 




4000 (3) 






















4010 




•• 


4024 


(2) 


4008 (2) 


4008 


(5) 


4008 


(2) 


4008 (1) 


4025 (3) 




, t 


4025 


(1) 


4025 (3) 


4025 


(6) 


4025 


(4) 


4025 (4) 


4041 (1) 




. , 








4040 


(2) 








4054 (2) 






















4067 (2) 






. . 




. • 


4069 


(2) 


4069 


(2) 


4069 (2) 


. » 


, . 


. . 


. , 






4071 


(2) 








, . 


. . 


. . 


. , 






4075 


(2) 


4075 


(2) 


4075 (2) 


4086 (1) 




•• 








• 




4088 
4094 


(5) 
(2) 




H 6 4101 (6) 


4101 


4101 


410L* 


(6) 


4101* " (6) 


4101* 


(6) 


4101 


(6) 


4101 (6) 


, . 


. , 


. . 






. . 


4104 


(2) 








, . 


, , 


. . 








. 




4114 


(4) 




. , 


» , 


. . 


, , 






4119 


(2) 








4120 (1) 


• * 


• • 


412P5 

4L27 


(2) 
(3) 


4120-5 (2) 
4127 (3) 


4120-1 


(4) 


4120-f 


(2) 


4120-5 (2) 


4129 (I) 


. . 


. . 


4130 


(3) 


4130 (3) 












4142 (1) 


4143 


4] 43 


4143 


(1) 


4143 (2) 


4143 


(5) 


4143 


(2) 


4143 (2) 


4154 (2) 






















4167 (1) 


. . 


. » 


. , 




, . 


4168 


(3) 








. . 


, . 


. , 


4172 


(4) 


4172 (1) 


4172 


(1) 








. . 


. . 


. . 


4177 


(4) 


4177 (1) 


4177 


(1) 








4204 (1) 






















4226 (1) 






















4234 (1) 


4233 


4233 


4233 


(5) 


4233 (2) 


. 










. , 


. , 


, , 


4241-c 


(2) 


, . 


4241-5 


(2) 








, . 


, . 


, . 


, . 




, . 


4253 


(2) 








4269 (2) 




•• 


4298' 


(3) 


4267 (2) 


4267 


(4) 


4267 


(1) 


4267 (1) 


• • 


. . 


, . 


4302 


(3) 














, . 


, , 


, , 


4307 


(3) 














, . 


, , 


, , 


4314 


(3) 




• < 




4314 


(1) 


4314 (1) 


. . 


, . 


, . 


4337 


(2) 














H v 4340(6) 


4340 


4340 


4340 


(6) 


4340 (6) 


4340 
4345 


(6) 
(2) 


4340 


(6) 


4340 (6) 


. . 


. . 


. . 


4351 


(4) 


4351* ' (1) 


4351 


(2) 


4351 


(1) 




43S5 (1) 


43S3 


4383 


4383 


(3) 












(4) 


4389 (2) 


43S8 


4388 


4388 


(1) 


4388 (3) 


4388 


(5) 


4388 


(2) 


4388 


. . 


, , 


, . 


4394-3 


(3) 


, , 


43943 


(2) 








4410 (1) 






















•• 


•• 


•• 


• • 




•• 


4414-5 


m 


4414-5 


(1) 4414-5 (3) 



SPECTRUM OF THE GREAT NEBULA IN" ORION. 



87 



Table IV. — Comparison of Orion Nebula with Stars of Groups II. and III, 
(Region K to \ 472 Angstrom) — (continued.) 













Group III-/. 






Orion nebula. 


Group II. 


Group Ilia. 






























a. Cygni. 


Rigel. 


Bellatrix. 


c Oriouis. 


a. Virginis. 








4117 (3) 




4417 (2) 








4426 (2) 






















. . 


. , 


, , 


4437 (3) 








4471 (4) 


4471 


4471 


4471 (1) 
4481 (5) 


4471 (4) 

4481 (5) 


4471 (6) 
4481 (3) 


4471 


(5) 


4471 (4) 


4495 (4) 


















4539 (2) 


4541 


4541 


4541 (2) 
4549 (4) 


., 


•• 


4541 


(1) 


4541 (1) 








4555-5 (3) 


, . 


4553 (3) 








. . 


. . 




4558-5 (3) 
















, , 


4583 (4) 












4627 (2) 


4629 


4629 


4629 (3) 


. , 


4629 (2) 








4715 










4714 (3) 









In the accompanying map (fig. 4) an attempt is made to show the gradual change 
of the bright lines of the nebulae and bright-line stars into dark ones as condensation 
proceeds. Not all the lines seen in the various spectra, but only those which best 
illustrate the results of progressive condensation, are dealt with. In the spectrum of 
the Orion nebula and planetary nebulse, the lines shown in the map are those which 
afterwards appear as bright lines in the bright-line stars, or as dark lines in some of 
the more condensed bodies. The lines mapped as belonging to the bright-line stars 
are those which appear twice in Professor Pickering's lists, to which reference has 
been made, except in the case of the important line at A 4471, which has been 
included because it appears in P Cygni as well as in one of Pickering's types of 
bright-line stars. The dark lines shown in the spectra of stars of Groups II., Ilia., 
III/3., Illy., IVa., and TV/3.,'" are only those which show remarkable coincidences 
either amongst themselves or with the bright lines at the foot of the map. The 
approximate intensities of the various lines in the map are represented by their 
thicknesses. 

If we consider, first, the question of the hydrogen lines, it will be seen that they 
begin to thin out as bright lines in the brightdine stars, and make their appearance 
as thin dark lines in Group II. From Group II. to Group IV. they thicken pretty 
regularly ; but other causes besides temperature may possibly affect their apparent 
thickness, as I have previously pointed out.t 

In addition to the lines of hydrogen, other lines, including the H and K lines of 

* See ' Phil. Trans.,' vol. 184, 1893, p. 725. 
t Ibid., p. 688. 



88 



PEOFESSOR J. N. LOCKYER ON THE PHOTOGRAPHIC 



calcium, and the lines at X 4388 and X 4471, appear as dark lines at an early stage in 
Group II. 

Other lines, however, do not appear dark until a later stage ; X 4025, X 4069, and 
X 4269, for example, do not make their appearance as dark lines until Group Illy., 
and others, such as X4205, do not appear until Group IV. is reached. 

Some of the dark lines, as X4025 and X4471, have their maximum intensity in 
Group Illy., whilst others are much less regular in their intensities in passing through 
the different groups. 



CRIV,i 



a flflHNts 
j * oaiowe 

CR.Hly < ' " 



■ i 



CR.I!I„ 



CR.tll™ aTAUR! 



Cft. II a omoNis 



' I 

41 



1. 




CR.I,-. BM UNE STA 



CRJ a ORION NEBULA 



CR.Ir, PLAN NEBLL*: 



Fig. 4. Diagram showing the gradual change of bright to dark lines in condensing swarms of meteorites. 



In general, it may be taken that the absence of some of the lines from Group II. 
and the eailier stages of Group III. is due to the approximate equality of the 
radiating and absorbing areas of the vapours producing such lines. 

With the aid of a series of photographs taken with special exposures, it is possible 
to extend the comparison of the stars of Groups III/3. and Illy, with the nebula into 
the ultra-violet region of the spectrum. These photographs have been reduced by 
Mr. Shackleton. The coincidences are shown in Table V. In this table Groups II. 



SPECTRUM OF THE GREAT NEBULA IN ORION. 89 

and III. are omitted, for the reason that their spectra beyond K are only photo- 
graphed with great difficulty.* 

The wave-lengths of the lines of the nebula are copied from Table I., and are 
expressed on Cornu's scale ; those of the lines in the ultra-violet spectra of stars of 
Group III. are based on wave-lengths of the ultra-violet lines of hydrogen on 
Rowland's scale, according to Professor Hale.1' 

The wave-lengths have been left in these different scales, because the differences 
are only minute, and, in general, in the ultra-violet region, less than the assumed 
accuracy of the wave-lengths as determined by the instruments at our disposal. 



* ' Phil. Trans.,' A, vol. 184, IS93, p. 701. 

t ' Astr. and Ast.-Phys.,' vol. 11, 1892, p. 618. 



MDCCCXCV, 



90 



PROFESSOR J. N". LOCKYER ON THE PHOTOGRAPHIC 



Table V. — Comparison of the Orion Nebula with Stars of Group III. in the 

Ultra- Violet Region. 





- 




Group IH7. 






Orion nebula. 












a. Cygni. 


Rigel. 


Bellatrix. 


c Orionis. 


a Virginia. 


3707 (2) 






3711-8 (Hr) 


37118 (HO 




3715 (1) 






3721-9 (H/0 


3721-9 (H/,) 




3729 (6) 






3734-2 (H\) 


3734-2 (HX) 




3743 (1) 












(Hi) 3752 (1) 






3750-2 (H«) 


3750-2 (H K ) 




(Hi) 3770 (1) 






3770-8 (Hi) 


3770-8 (Hi) 




(He) 3796 (2) 


3798-1 (He) 


3798-1 (He) 


37981 (He) 
3806-6 


3798-1 (He) 
3806 


3798-1 (He) 






3819-5 


38195 


3819-5 






3820-2 












3827-8 












3829-5 












3832-0 










(HO 3833 (2) 


3835-5 (H v ) 

3838-3 

3840-4 

3845-5' 


3835-5 (H v ) 
38427 


3835-5 (HO 


3835-5 (H 7 ) 


3835-5 (H,) 


3847 (1) 


3849-6 
3853-6 


3853-6 








3855 (1) 


3856-1 
3859-5 
3862-8 
3865-6 


3856- 1 




3856 
3862-8 








3867-9 


3867-5 


3867 




3868 (4) 


3869-8 

3878-7 
3882-5 


3871-7 


3871-2 
3876-5 






(Hi;) 3887 (4) 


3889-14 (HC) 
3900-8 


3889-1 (Hi;) 


3889-1 (HD 


3889-1 (HiT) 


3889-1 (Hf) 


3902 (2) 


3903-4 
3906-2 
39135 
3918-8 

3930-2 
39318 




3919-2 

3921 

3926-7 


3929-4 
39312 




3933 


39336 


3933-6 


3933-6 


3933-6 


3933-6 



SPECTRUM OF THE GREAT NEBULA IN ORION. 91 

VI. General Conclusions. 

(1) The spectrum of the nebula of Orion is a compound one consisting of hydrogen 
lines, low temperature metallic lines and flutings, and high temperature lines. The 
mean temperature, however, is relatively low.""' 

(2) The spectrum is different in different parts of the nebula. 

(3) The spectrum bears a striking resemblance to that of the planetary nebulae and 
bright-line stars. 

(4) The suggestion, therefore, that these are bodies which must be closely 
associated in any valid scheme of classification is strengthened. 

(5) Many of the lines which appear bright in the spectrum of the nebula appear 
dark in the spectra of stars of Groups II. and III., and in the earlier stars of 
Group IV. ; and a gradual change from bright to dark lines has been found. " 

(6) The view, therefore, that bright-line stars occupy an intermediate position 
between nebulae and stars of Group III. is greatly strengthened by these researches. 

I have to express my great obligations to Mr. Fowler for the zeal and patience 
which he displayed in taking the photographs under somewhat unfavourable con- 
ditions. He is responsible for the determination of the wave-lengths of the lines and 
has assisted in the discussion. 

Messrs. Baxakdael and Shackleton, computers to the Solar Physics Committee, 
have assisted in the preparation of the tables and the map illustrating the changes of 
spectrum with increasing condensation. 



' Roy. Soc. Pioc.,' vol. 43, p. 152, 1887. 



N 2 



[ 93 ] 



III. Propagation of Magnetization of Iron as affected by the Electric Currents 

in the Iron. 

By J. Hopkinson, F.R.S., and E. Wilson.* 

Received May 17, — Read May 31, 1894. 

Part I. 

It is not unfamiliar to those who have worked ou large dynamos with the ballistic 
galvanometer, that the indications of the galvanometer do not give the whole changes 
which occur in the induction. Let the deflections of the galvanometer connected to 
an exploring coil be observed when the main current in the magnetic coils is reversed. 
The first elongation will be much greater than the second in the other direction, and 
probably the third greater than the second — showing that a continued current exists 
in one direction for a time comparable with the time of oscillation of the galvanometer. 
These effects cannot be got rid of, though they can be diminished by passing the 
exciting current through a non-inductive resistance and increasing the electromotive 
force employed. This if carried far enough would be effective if the iron of the cores 
were divided so that no currents could exist in the iron; but the currents in the iron, 
if the core is solid, continue for a considerable time and maintain the magnetism of 
the interior of the core in the direction it had before reversal of current. It was one 
of our objects to investigate this more closely by ascertaining the changes occurring at 
different depths in a core in terms of the time after reversal has been made. 

The experiments were carried out in the Siemens Laboratory, King's College, 
London ; and the electro-magnet used is shown in fig. 1. It consists in its first form, 
the results of which though instructive are not satisfactory, of two vertical wrought- 
iron cores, 18 inches long and 4 inches diameter, wound with 2595 and 2613 turns 
respectively of No. 16 B.W.G. cotton-covered copper wire — the resistance of the two 
coils in series being 16 '3 ohms. The yoke is of wrought-iron 4 inches square in 
section and 2 feet long. The pole-pieces are of wrought-iron 4 inches square, and all 
surfaces in contact are truly planed. One of the pole-pieces is turned down at the 
end, wmich butts on the other pole-piece, for half an inch of its length to a diameter 
of 4 inches ; and three circular grooves are cut in the abutting face having mean 

* The experimental work of this paper was in pari carried out by three of the Student Demonstrators 
of the Siemens Laboratory, King's College, London, Messrs. Brazil, Atchison, and Gtreexhaji. We 
wish to express our thanks to them for their zealous co-operation. 

l'J.2.95 



94 



MESSRS. J. H0PK1NS0N AND E. WILSON ON THE 







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PROPAGATION OF MAGNETIZATION OF IRON. 



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96 MESSRS. J. HOPKINSON AND E. WILSON ON THE 

diameters of 2 4 G, 5"16, and 7*75 centims. respectively, for the purpose of inserting 
copper coils the ends of which are brought out by means of the radial slot shown in 
fig. 2. When the pole-pieces are brought into contact as shown in fig. 1, we have 
thus three exploring coils within the mass and a fourth was wound on the circular 
portion outside. These exploring coils are numbered 1, 2, 3, 4 respectively, starting 
with the coil of least diameter. 

Fig. 3 gives a diagram of the apparatus and connections, in which A is a reversing 
switch for the purpose of reversing a current given by ten storage cells through the 
magnet windings in series ; B is a Thomson graded galvanometer for measuring 
current; and C is a non-inductive resistance of about 16 ohms placed across the 
magnet coils for the purpose of diminishing the violence of the change on reversal. 
The maximum current given by the battery was 1*2 amperes. A DArsonval gal- 
vanometer of Professor Aybton's type, D, of 320 ohms resistance ; a resistance 
box E ; and a key F were placed in circuit with any one of the exploring 
coils 1, 2, 3, 4, for the purpose of observing the electromotive force of that circuit. 
The method of experiment was as follows : — The current round the magnet limbs was 
suddenly reversed and readings on the DArsonval galvanometer were taken on each 
coil at known epochs after the reversal. The results are shown in fig. 4, in which 
the ordinates are the electromotive forces in C.G.S. units and the abscissas are in 
seconds. 

The portion of these curves up to two seconds was obtained by means of a ballistic 
galvanometer having a periodic time of fifty seconds, the key of its circuit being 
broken at known epochs after reversal. From the induction curve so obtained the 
electromotive force was found by differentiation. 

The curve A which is superposed on curve 4 of fig. 4 gives the current round the 
magnet in the magnetizing coils. It is worth noting, that, as woidd be expected, it 
agrees with the curve 4. The potential of the battery was 1"2 amperes X 16*3 ohms 
= 19 - 6 volts. Take the points two seconds after reversal, the electromotive force in 
one coil is 330,000 ; multiplying this by 5208, the number of coils on the magnet, we 
have in absolute units 1,718,640,000 as the electromotive force on the coil due to 
electromagnetic change, or, say, 17'2 volts. Subtracting this from 19'6 we have 2*4. 
The electromotive force observed is *125 X 16"3 = 2 - 02. The difference between 
these could be fully accounted for by an error of ^ second in the time of either 
observation. 

The general character of the results was quite unexpected by us. Take cod No. 2 
for example, the spot of light, on reversing the current in the magnet winding, would 
at once spring off to a considerable deflection, the deflection would presently diminish, 
attaining a minimum after about 6 seconds ; the deflection would then again increase 
and attain a maximum greater than the first after 8 seconds, it would then diminish 
and rapidly die away. 

To attempt a thorough explanation of the peculiarities of these curves would mean 



PROPAGATION OF MAGNETIZATION OF IRON. 97 

solving the differential equation connecting induction with time and radius in the iron 
with the true relation of induction and magnetizing force. But we may inversely from 
these curves attempt to obtain an approximation to the cyclic curve of induction of 
the iron. 

Let I be the mean length of lines of force in the magnet. Let n be the number of 
convolutions on the magnet, and let c be the current in amperes in the magnetizing 
coils at time t. Then at this epoch the force due to the magnetizing coils is 4irnc/10?. 
Call this H r 

Next consider only one centimetre length of the magnet in the part between the 
pole-pieces which is circular and has coils 1, 2, 3, wound within its mass, and coil 
4 wound outside. The area of each of the electromotive force curves of the coils 1, 2, 

3, 4, up to the ordinate corresponding to any time, is equal to the total change of the 
induction up to that time. 

In tig. 2 let A 1( A 2 , A 3 , A 4 be the areas in sq. centims. of coil 1 and the ring-shaped 
areas included between the coils 1, 2, 3, 4 respectively. Then the induction at time t, 
as given by the integral of curve 1, divided by A x is the average induction per 
sq. centim. for this epoch over this area. Also, the induction at time t, as given by 
the integral of curve 2, minus the induction for the same time, as given by the 
integral of curve 1, divided by A 2 , is the average induction per sq. centim. for this 
area. Similarly, average induction per sq. centim. for A 3 , A 4 can be found for any epoch. 

Consider* area A x . It is obvious that all currents induced within the mass 
considei-ed external to this area, due to changes of induction, plus the current in 
the magnetizing coil per centim. linear, at any epoch, go to magnetize this area, and, 
further, the induced currents in the outside of the area A 1 itself go to magnetize the 
interior portion of this area. We know the electromotive forces at the radii 1, 2, 3, 

4, and the lengths in centims. of circles corresponding to these radii. From a know- 
ledge of the specific resistance of the iron we can find the resistance, in ohms, of rings 
of the iron corresponding to these radii, having a cross-sectional area of 1 sq. centim. 
Let these resistances be respectively r r , r 2 , r s , r 4 . At time t, let e x , e % , <? 3 , e 4 be the 

electromotive forces in volts at the radii 1, 2, 3, 4. then — , — " - , — , — are at this 

r i r i r i r i 

epoch the amperes per sq. centim. at these radii. Let a curve be drawn for this epoch, 
having amperes per sq. centim. for ordinates and radii in centims. for abscissa?. Then 
the area of this curve, from radius 1 to radius 4, gives approximately the amperes per 
centim. due to changes of induction, and (neglecting the currents within the area 
considered) the algebraic sum of this force (call it H 2 ), with the force due to the 
magnetizing coils (ILJ at the epoch chosen, gives the resultant magnetizing force 
acting upon area A x . If H is this resultant force, we have 11 = 11! + H 2 . Next 
draw a curve showing the relation between the induction per sq. centim. (B) and the 
resultant force (H) for different epochs. This curve should be an approximation to 
the cyclic curve of induction of the iron. 
MDCCCXCV. — A. O 



98 



MESSRS. J. H0PK1NS0N AND E. WILSON ON THE 
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100 MESSRS. J. HOPKINSON AND E. WILSON ON THE 

The attempt to obtain an approximation to the cyclic curve of induction from the 
curves in fig. 4 was a failure, that is to say, the resulting curve did not resemble a 
cyclic curve of magnetization. This is due to imperfections of fit of the two faces, in 
one of which the exploring coils are imbedded. That this imperfection of fit will tend 
to have a serious effect upon the distribution of induction over the whole area is 
obvious on consideration. Take the closed curve abed in fig. 5, where AB is the 
junction between the pole pieces. If the space between the faces was appreciable, the 
force along be and ad in the iron could be neglected in comparison with the forces in 
the non-magnetic spaces ab, cd. The magnetizing force is sensibly inc, where c is the 
current passing through the closed curve. This may be made as small as we please. 
Therefore, the force along ab is equal to the force along dc. In our case the space 
between the faces is very small, but has still a tendency towards an equalizing of 
the induction per unit area over the whole surface. 

To test this the following experiment was tried. At a distance of 2|- inches from 
the abutting surfaces of the pole pieces four holes were drilled in one of the pole 
pieces in a plane parallel with the abutting surfaces, as shown in fig. 6. By means of 
a hooked wire we were able to thread an insulated copper wire through these holes, 
so as to enclose only the square area A, which is bounded by the drilled holes and has 
an area of '61 sq. inch. The wire is indicated by the dotted lines. Fig. 7 gives two 
curves taken by the D'Arsonval in the manner already described for a revei'sal of the 
same current in the copper coils of the magnets. No. 1 (fig. 7) is the curve obtained 
from No. 1 coil (fig. 2) near the air space. No. 2 (fig. 7) is the curve obtained from 
the square coil shown in fig. 6. The difference is very marked and shows at once the 
effect of the small non-magnetic space which accounts for the large initial change of 
induction previously observed on the coils 1,2, 3 in fig. 4. Similar holes were drilled 
in the yoke of the magnet in a plane midway between the vertical cores, having the 
same area of "61 sq. inch ; and on trial exactly the same form of curve was produced 
as is shown in No. 2 of fig. 7. This method of drilling holes in the mass is open to 
the objection that the form of the area is square. 

Whilst the above experiments were being made the portion of the magnet to take 
the place of the pole-pieces previously used was being constructed as follows : — In 
fig. 8 the portion of the magnetic circuit resting upon the vertical cores consists of a 
centre rod A 1 of very soft Whitworth steel surrounded by tubes A 2 , A 3 of the same 
material. The diameter of A x is 1 inch. The outside diameter of A 2 is 2- 1 ,- inches ; 
and A 3 is 4 inches outside diameter between the cores of the magnet, but is 4 inches 
square at each end where it rests upon the magnet limbs. At the centre of the rod 
-A-i (longitudinally) a circular groove is turned down 1 millim. deep and 5 millims. 
wide, and also a longitudinal groove 1 millim. deep and 1 millim. wide is cut as 
shown in the figure for the purpose of leading a double silk covered copper wire from 
terminal T l to 9 convolutions at the centre and along the rod to terminal T 2 . A 
similar groove is cut in the outside of the tube A 2 , and a copper wire is carried from 



PROPAGATION/ OF MAGNETIZATION" OF IRON. 



101 



terminal T 3 to 9 convolutions round the centre of the tube again along the groove to 
terminal T 4 . Nine convolutions were also wound round the outside tube A 3 , the ends 
of which are connected to the terminals T 5 , T 6 respectively. 

The tubes and rod were made by Sir J. Whitworth and Co., of Manchester, 
and a considerable force was required to drive the pieces into their proper position. 
Our best thanks are due to Professor Kennedy and his assistants for the putting 
together of these pieces by means of a 50-ton hydraulic testing machine. We are 
aware that the surfaces are somewhat scored by the hydraulic pressure, and the 
magnetic qualities may be slightly different for layers of the soft steel near these 
surfaces, but they serve just as well for the purpose of our experiments. 

Fig. 8. 




Systematic experiments were then commenced. The magnetizing coils on the 
magnets were placed in parallel with one another, and a total current of 1*75 amperes 
(that is, '87 ampere in each coil), due to 5 storage cells, was reversed through the 
coils. The arrangement of apparatus is shown in fig. 3, except that the pole-pieces 
are replaced by the soft steel tubes shown in fig. 8, and the non-inductive resistance 
C is removed. We have now three exploring coils instead of four, and these are 
marked 1, 2, 3 respectively, starting with the coil of smallest diameter. For the 
purpose of obtaining the current curve, the D'Arsonval was placed across a non- 
inductive resistance of ^ ohm in the circuit of the magnetizing coils. Fig. 9 gives 
a set of curves obtained with the 5 cells, and also another set obtained by a reversal 
of 1*8 amperes given by 54 cells — a non-inductive resistance being placed in the 
circuit to adjust the current. 

The effect of reversing the same maximum current with two different potentials is 
very marked. Take coil No. 1. With 5 cells the maximum rate of change of 
induction occurs at 9 seconds after reversal, at which epoch the current in the copper 
coils is about 1 ampere, the maximum current being l - 75. With 54 cells the 
maximum rate of change of induction occurs at 4 seconds, and here the current in the 
copper coils is nearly a maximum. We therefore chose to work with 54 cells, thus 
avoiding a magnetizing force due to the current in the copper coils varying for 
considerable times after reversal. 



102 



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104 MESSRS J. HOPKINSON AND E. WILSON ON THE 

Table I. gives a list of the experiments made with total reversal of current due to 
54 cells, the magnetizing coils being kept in parallel with one another, and the 
magnitude of current through them adjusted by means of a non-inductive resistance. 

In fig. 10 the maximum current in the copper coils is "0745 ampere, which, after 
reversal, passes through zero and attains a maximum at about 3 seconds. It will be 
observed that the change of induction with regard to each of the coils 1, 2, 3 is 
rapid to begin with, but that it gradually decays and becomes zero at about 46 seconds 
after reversal. 

Fig. 11 is interesting in that it gives the particular force at which coils 1 and 2 
show a second rise in the electromotive force curves, No. 1 being a maximum at 
about 25 seconds, and No. 2 at about 8 seconds after reversal. These "humps" 
become a flat on the curve for a little smaller force, and, as shown in fig. 10, 
they have disappeared altogether. In this case the current in the copper coils has 
attained a maximum at about 4 seconds after reversal. 

In fig. 12 the maximum current in the copper coils is "24 ampere, corresponding 

4ir 2600 x -24 

with a force in C.G.S. units of 4'96. This is e - ot from — - — — . The current 

s 10 lt>8 

in the copper coils has attained its maximum value at about 4 seconds after 

reversal, and changes of induction were going on up to 35 seconds. 

In the following attempt to obtain an approximation to the cyclic curve of 
hysteresis, from these curves, we have taken the volunie-sjDecific resistance of the 
soft steel to be 13 X 10 ~ 6 ohm. We have taken the diameter of coils 1, 2, 3 to be 
respectively 1*22, 3*18, and 5'08 centims.,* and we find that the corresponding- 
resistances, in ohms, of rings of the steel having 1 sq. centim. cross-section and 
mean diameters equal to the coils are, respectively, 103*7 XlO -6 , 259"4X10 -6 , and 
416"4X 10 -c . From a knowledge of the electromotive forces at the three radii, for 
a given epoch, we are able to find the amperes per sq. centim. at those radii. In fig. 
12a a series of curves have been drawn for different epochs, giving the relation 
between amperes per sq. centim. and radii in centims., and the areas of these curves 
between different limits have been found, and are tabulated in Table II. It is 
necessary here to state that the path of these curves through the four given points 
in each case is assumed ; we have simply drawn a fair curve through the points. 
But what we wish to shew is that the results obtained with the curves, drawn as 
shown in fig. 12a, are not inconsistent with what we know with great probability to 
be true. 

The results shown in fig. 12b have been obtained as follows : take curve I. 
fig. 12b ; the electromotive force curve of coil 1, fig. 12, has been integrated, 
and the integral up to the ordinate corresponding to any time is equal to the total 

* In Part II. of tliis paper the smallest radius was taken to be 1"27. For our purpose the difference 
is not worth the expense of correction. 



PROPAGATION OP MAGNETIZATION OF IRON. 105 

change of the induction up to that time, which divided by the area of the coil in sq. 
centims. gives the average induction per sq. centim. In obtaining the areas we had 
to assume the path of the electromotive force curve up to 2 seconds, but this we can 
do with a good deal of certainty. 

With reo-ard to the forces we see that after 3 seconds the induced currents have 
to work against a constant current in the copper coils. In obtaining the forces due 
to induced currents we have only taken the area of the curves in fig. 12a between 
the radii 1"22 centims. and 5 '08 centims. ; that is, we have neglected the effect of 
the currents within the area of coil No. 1 altogether. The resultant force (H) is 
the algebraic sum of the force (H 3 ) due to the currents between the radii taken, and 
the force (rlj) due to the current in the copper coils, and is set forth for different 
epochs in Table II. The inductions per sq. centim. have been plotted in terms of 
this resultant force (H), and curve I., fig. 12b, shows this relation. 

Next, take curves II. and III., fig. 12b. In obtaining the inductions for these 
curves, the difference between the integrals of curves No. 1 and 2, fig. 12, for a given 
epoch, has been taken. This gives the induction for this epoch, which, when divided 
by the ring-shaped area between coils 1 and 2, gives the average induction per unit 
of that area. 

In obtaining the forces in curve II., fig. 12b, we have taken the areas of the curves in 
fig. 12a between the radii 3"18 centims. and 5"08 centims. ; that is, we have neglected 
the forces within the area under consideration as before. Here the error is of more 
importance, and may partly account for the difference between the forces of 
curves I., II. In curve III. we have taken the areas of curves in fig. 12a between 
the radii 2 "2 and 5 '08 ; that is, we have taken account of the force due to induced 
currents over a considerable portion of the area considered. Coupled with the 
uncertainty in form of the curves in fig. 12a we have the uncertainty as to how 
much to allow for the forces due to induced currents over the particular area 
considered. The difference in the ordinates of curves I. and II. may partly be 
accounted for by errors arising from the assumed path of the electromotive force 
curve up to 2 seconds, which is more uncertain in curve 2, fig. 12, than in curve 1 ; 
and partly to possible slight inequality between the materials of the rod and its 
surrounding tube. 

In fig. 13 the maximum current in the copper coils is '77 ampere, corresponding 
with a force in C.G.S. units of 16. The current in the copper coils, after passing 
through zero, attains its full value at about 9 seconds after reversal, and the change 
of induction ceases at 10 seconds. 

No. 1 curve, fig. 13, has been integrated, and the maximum induction per 
sq. centim. found to be 14,500 C.G.S. units. We have taken a given cyclic curve 
for soft iron corresponding with this maximum induction, and have tabulated the 
forces obtained therefrom in Table III. for the different values of B got from the 
integration of No. 1 curve. We then plotted in fig. 13a the amperes per sq. centim. 

mdcccxcy.— a. p 



106 



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108 MESSRS. J. HOPKINSON AND E. WILSON ON THE 

at the different radii for different epochs, and in each case, by drawing a curve fairly 
through them, we were able to produce areas in fair correspondence with areas as 
got by means of the given cyclic curve. The comparative areas are tabulated in 
Table III. 

In fig. 9 the maximum current in the copper coils due to the 54 cells is 
1*8 amperes, corresponding with a force of 207 in C.G.S. units. In this case the 
current had passed through zero and attained a maximum at 6 seconds after reversal ; 
the change of induction being zero also at this time. We have worked out the 
current per sq. centim. for the different radii at different epochs, as before, and have 
plotted them in fig. 9a. Fig 9b gives the relation of B to H, found from the curves, 
and it also shows a fair approximation to the cyclic curve for soft iron, although in 
this case the points are fewer in number and were more difficult to obtain, owing to 
the greater rapidity with which the D'Arsonval needle moved as compared with the 
earlier curves. 

With a reversal of 2 - 3 amperes the whole induction effects had died out at 
5 seconds after reversal. Coil No. 1 showed a maximum electromotive force at about 
3ig seconds. Coil No. 2 gave a dwell, and attained a maximum at 2 seconds, and 
then died rapidly away. Coil No. 3 attained an immediate maximum and died 
rapidly to zero at 5 seconds. 

With a reversal of 6^ amperes the whole inductive effects had died out at about 
3 seconds after reversal. No. 1 coil showed a maximum electromotive force at about 
If seconds. No. 2 gave a dwell and attained a maximum at about 1-| seconds and 
rapidly died away to zero at about 2 seconds. No. 3 attained an immediate maximum 
and died rapidly to zero at about 2 seconds. 

The variations in form of these curves and of the times the electromotive forces 
take to die away are intimately connected with the curve of magnetization of the 
material. When the magnetizing force is small (l"7) the maxima occur early because 
the ratio induction to magnetizing force is small. As the magnetizing force increases 
to 3 and 4 - 96 the maxima occur later because this ratio has increased, whilst when 
the force is further increased to 16 and 37'2, as shown in figs. 13 and 9, the maxima 
occur earlier because the ratio has again diminished. 

The results, both of these experiments and of those which follow, have a more 
general application than to bars of the particular size used. From the dimensions 
of the partial differential equation which expresses the propagation of induction in 
the bar, one sees at once that if the external magnetizing forces are the same in two 
bars differing in diameter, then similar magnetic events will occur in the two bars, 
but at times varying as the square of the diameters of the bars. But one may see 
this equally without referring to the differential equation. Suppose two bars, one 
n times the diameter of the other, in which there are equal variations of the 
magnetizing forces ; consider the annulus between radii r } , r z and ni\, m\ in the two, 
the resistance per centimetre length of the rods of these annuli will be the same for 



PROPAGATION OF MAGNETIZATION OF IRON. 109 

their area, and their lengths are alike as 1 : n ; the inductions through them, when 
the inductions per centimetre are the same, are as the areas, that is, as 1 : n 3 . Hence 
if the inductions change at rates inversely proportional to 1 : n 3 , the currents between 
corresponding radii will be the same at times in the ratio of 1 : n 2 , and the magnetizing 
forces will also be the same. 

Magnets of sixteen inches diameter are not uncommon ; with such a magnet, the 
magnetizing force being 37 and the magnetizing current being compelled to at once 
attain its full value, it will take over a minute for the centre of the iron to attain its 
full inductive value. 

On the other hand, with a wire or bundle of wires, each 1 millim. diameter, and 
a magnetizing force between 3 and 5, which gives the longest times with our bar, 
the centre of the wire will be experiencing its greatest rate of change in about 
yoo second. This is a magnetizing force similar to those used in transformers, and 
naturally leads us to the second part of our experiments. 

Part II. — Alternate Currents. 

This part of the subject has a practical bearing in the case of alternate current 
transformer cores, and the armature cores of dynamo-electric machines. 

The alternate currents used have periodic times, varying from 4 to 80 seconds, and 
were obtained from a battery of 54 storage cells by means of a liquid reverser,* shown 
in elevation and plan in figs. 14 and 15. It consists of two upright curved plates of 
sheet copper, AA, between which were rotated two similar plates, BB, connected 
with collecting rings, DD, from which the current was led away by brushes to the 
primary circuit of the magnet. The copper plates are placed in a weak solution of 
copper sulphate in a porcelain jar. The inner copper plates, and the collecting rings, 
are fixed to a vertical shaft, S, which can be rotated at any desired speed by means 
of the gearing shown in the figure. The outer plates are connected to the terminals 
of the battery of storage cells, and the arrangement gives approximately a sine curve 
of current when working through a non-inductive resistance. 

The experiments were made with the same electro-magnet and Whitworth steel 
tubes described in Part I. of this paper. Fig. 16 gives a diagram of connections in 
which M is the current reverser, G is the Thomson graded current meter for 
measuring the maximum current in the copper coils, and W is the electro-magnet. A 
small, non-inductive resistance, placed in the primary circuit served to give the curve 
of current by observations on the D'Arsonval galvanometer, D, of the time variation 
of the potential difference between its ends. The D'Arsonval galvanometer was also 
used, as in Part I., for observing the electromotive forces of the exploring coils 1, 2, 
and 3 (see tig. 8, Part I.), E, being an adjustable resistance in its circuit for the 
purpose of keeping the deflections on the scale. 

* This form of l-everser is due to Professor Ewimg. 



110 



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112 MESSRS. J HOPKINSON AND E. WILSON ON THE 

The method of experiment was as follows : — The liquid reverser, M, was placed so 
as to give a maximum current on the meter G, which was adjusted by non-inductive 
resistance, N, to the desired value, and, in all cases, when changing from higher to 
lower currents, a system of demagnetization by reversals was adopted. Time was 
taken, as in Part I., on a clock beating seconds, which could be heard distinctly. 

As an example, take fig. 19, in which the periodic time is 80 seconds, and the 
maximum current in the copper coils "23 ampere. The E.M.F. curves of the exploring 
coils are numbered 1, 2, and 3 respectively, and the curve of current in the copper 
coils is also given. 

As in the case of simple reversals (Part I.) we may from these curves attempt to 
obtain an approximation to the cyclic curve of induction of the iron. In all cases 
where this is done we have taken coil 1 and considered the area- within it — that is to 
say, from a knowledge of the E.M.F. 's at different depths of the iron, due to change 
of induction at any epoch, we have estimated the average magnetizing force acting in 
this area, and this we call H 3 . The curves from which these forces have been 
obtained are given in fig. 19a, and have been plotted from Table VI. The algebraic 
sum of this force, H 2 , and the force H l5 given at the same epoch by the current in 
the copper coils, is taken to be the then resultant force magnetizing this area. Also 
the integral of curve 1, fig. 19, gives the average induction over this area at the same 
epoch. Curve x, fig. 19b, is the cyclic curve obtained by plotting the inductions in 
terms of the resultant force H. 

A word is necessary with regard to the last column in Table VI. This gives the 
total dissipation of energy by induced currents in ergs per cycle per cub. centim. of 
the iron. We know the watts per sq. centim. at different depths of the iron for 
different epochs. Let a seines of curves be drawn (fig. 19c) for chosen epochs giving 
this relation : the areas of these curves from radii to 5 "08 give for the respective 
epochs the watts per centim. dissipated by induced currents. In symbols this is 



ec 



dr ; where r is the radius, and ec the E.M.F. and current. It is now only 
J sq. centim. 

necessary to integrate with regard to time in order to obtain the total dissipation : we 

have chosen a half period as our limits. This gives us : — dr dt, and is got 

1 ° J J sq. centim. ° 

from the area of curve z, fig. 19d. The ordinates of this curve are taken from the 

last column of Table VI. 

The curves in figs. 21, 22, have been treated in a similar manner to that already 

described in connection with fig. 19. But in fig. 20 the procedure is a little different. 

In this case the periodic time is 20, and the maximum force per centim. linear, due to 

the current in the copper coils, is 4 - 87. With this frequency and current the effects 

of induced currents in the iron are very marked : we have taken a given soft 

iron cyclic curve, of roughly the same maximum induction as given by the integral of 

curve No. 1, fig. 20, and have tabulated the forces obtained therefrom in Table VII, 



PROPAGATION' OF MAGNETIZATION OF IRON. 113 

In fig. 20a we have plotted the amperes per sq. centiua. at the different radii, and for 
the sevei'al epochs, and in each case, by drawing a curve fairly through these points, 
as shown in the figure, we are able to produce areas in fair correspondence with the 
areas obtained by means of the given cyclic curve. The comparative areas are given 
in Table VII. 

The results shown in fig. 22 are by no means so satisfactory as the results given by 
other figures, but we have thought it better to insert them here, as we do not wish 
to make any selection of results which might give an idea of average accuracy greater 
than these experiments are entitled to. 

Referring now to the summary of results in Table V., we note the marked effect of 
change of frequency upon the average induction per unit area of the innermost coil 
No. 1, when dealing with comparatively small maximum inductions. Compare the 
results given in figs. 19 and 20. The maximum force per centim. linear due to the 
current in the copper coils is 4 - 8 in each case, but the average induction per 
sq. centim. of coil No. I is reduced from 7690 to 1630 by a change of frequency from 
TO t° iV This is, of course, not the case on the higher portion of the induction curve, 
as is shown by the results of figs. 21 and 22, although the resultant force H is 
reduced by the induced currents. 

In fig. 23 the maximum amperes in the copper coils is '24, and the periodic time is 
reduced to 4. An inspection of these curves shows the marked effect of change of 
frequency, coil No. 2 being exceedingly diminished in amplitude as compared with 
No. 3. 

As an example of the practical bearing of this portion of the paper, suppose we 
have a transformer core made out of iron wire, 1 millim. in diameter, the wires 
being perfectly insulated from one another. The outside diameter of our outer tube 

is 101 "6 millims. Similar events will therefore happen at times, varying as [77^r r 

Take the case of fig. 19. in which the periodic time is 80 seconds, and the maximum 
average induction per sq. centim. is about 7000. 

-= 129 periods per second, and this is an example which might arise in 

practice. The ergs dissipated per cycle per cub. centim. are 3820 by induced currents, 
and about 3000 by magnetic hysteresis. We see further, from fig. 20, that at 500 
periods per second only the outside layers of our 1 millim. wire are really useful. 

As another example, take the case of an armature core of a dynamo electric 
machine in which a frequency of 1000 complete periods per minute might be taken. 

In fig. 21 the periodic time is 80, and the maximum average induction per 

sq. centim. is 15,000. 

We have 

^ f = 80 (x/101-6) 3 

x = 101-6/36 = nearly 3 millims. 

MDCCCXCV. — A. Q 



114 



MESSRS. J. HOPKINSOX AND E. WILSON OX THE 



The ergs dissipated per cycle per cub. centim. are 26,000 by induced currents, and 
about 17,000 by magnetic hysteresis. This shows that according to good practice, 
where the wires in armature cores are of an order of 1 or 2 millims. diameter, the loss 
by induced currents would be but small as compared with the loss by magnetic 
hysteresis. This, of course, assumes the wires to be perfectly insulated from one 
another, which is not always realised in practice. 

Both the armature cores of dynamos and the cores of transformers are now usually 
made of plates instead of wire ; roughly speaking a plate in regard to induced 
currents in its substance is comparable to a wire of a diameter double the thickness 
of the plate. We infer that the ordinary practice of making transformer plates 
about -} millim. thick, and plates of armature cores 1 millim. thick, is not far wrong. 
Not much is lost by local currents in the iron, and the plates could not be much 
thicker without loss.* 

Table I. 





Maximum amperes in 
magnetizing coils. 


Maximum force in 

C.G.S. units. 

H 


1 

Maximum induction 
per sq. centim. 

rs 


Fig. 10 

„ 11 

„ 12, Table II. . 

„ 13, „ III. . 

,, y, ,, iv. . 


•0745 

•138 

•24 

•49 

•774 

1-80 

231 

6-5 


1-7 
30 

4-96 
101 
16-0 
37-2 
47-6 
1345 


8,000 
12,820 
14,495 
15,480 



* The question of dissipation of energy by local currents in iron has been discussed by Professors 
J. J. Thomson and Ewixg. See the ' Electrician,' April 8th and 15th, 1892. 



PROPAGATION OF MAGNETIZATION OF IRON. 



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MESSRS. J. ROPKINSON AND E. WILSON ON THE 



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PROPAGATION OF MAGNETIZATION OF IRON. 



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MESSRS. J. HOPKINSON AND E. WILSON ON THE 



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[ 123 ] 



IV. On the Dynamical Theory of Incompressible Viscous Fluids and the 

Determination of the Criterion. 

By Osborne Reynolds, M.A., LL.D., F.E.S., Professor of Engineering in Owens 

College, Manchester. 

Received April 25— Read May 24, 1894. 

Section I. 

Introduction . 

1. The equations of motion of viscous fluid (obtained by grafting on certain terms to 
the abstract equations of the Eulerian form so as to adapt these equations to the case 
of fluids subject to stresses depending in some hypothetical manner on the rates of 
distortion, which equations Navier* seems to have first introduced in 1822, and 
which were much studied by Cauchy+ and PotssonJ) wei'e finally shown by 
St. Venant§ and Sir Gabriel Stokes, || in 1845, to involve no other assumption than 
that the stresses, other than that of pressure uniform in all directions, are linear 
functions of the rates of distortion, with a co-efficient depending on the physical state 
of the fluid. 

By obtaining a singular solution of these equations as applied to the case of 
pendulums in steady periodic motion, Sir G. StokesI! was able to compare the 
theoretical results with the numerous experiments that had been recorded, with the 
result that the theoretical calculations agreed so closely with the experimental 
determinations as seemingly to prove the truth of the assumption involved. This 
was also the result of comparing the flow of water through uniform tubes with the 
flow calculated from a singular solution of the equations so long as the tubes were 
small and the velocities slow. On the other hand, these results, both theoretical and 
practical, were directly at variance with common experience as to the resistance 

* 'Mem. de 1'Academie,' vol. 6, p. 389. 

f 'Mem. des Savants Etrangers,' vol. 1, p. 40. 

J 'Mem. de 1'Academie,' vol. 10, p. 345. 

§ -B.A. Report,' 1846. 

|| ' Cambridge Phil. Trans.,' 1845. 

1 'Cambridge Phil. Trans.,' vol. 9, 1857. 

R 2 6.5.95 



124 PROFESSOR 0. REYNOLDS ON INCOMPRESSIBLE VISCOUS 

encountered by larger bodies moving with higher velocities through water, or by 
water moving with greater velocities through larger tubes. This discrepancy- 
Sir G. Stokes considered as probably resulting from eddies which rendered the 
actual motion other than that to which the singular solution referred and not as 
disproving the assumption.' 

In 1850, after Joule's discovery of the Mechanical Equivalent of Heat, Stokes 
showed, by transforming the equations of motion — with arbitrary stresses — so as to 
obtain the equations of (" Vis-viva") energy, that this equation contained a definite 
function, which represented the difference between the work done on the fluid by the 
sti'esses and the rate of increase of the energy, per unit of volume, which function, 
he concluded, must, according to Joule, represent the Vis-viva converted into heat. 

This conclusion was obtained from the equations irrespective of any particular 
relation between the stresses and the rates of distortion. Sir G. Stokes, however, 
translated the function into an expression in terms of the rates of distortion, which 
expression has. since been named by Lord Rayleigh the Dissipation- Function. 

2. In 1883 I succeeded in proving, by means of experiments with colour bands — 
the results of which were communicated to the Society* — that when water is caused 
by pressure to flow through a uniform smooth pipe, the motion of the water is direct, 
i.e., parallel to the sides of the pipe, or sinuous, i.e., crossing and re-crossing the pipe, 
according as Ll„„ the mean velocity of the water, as measured by dividing Q, the 
discharge, by A, the area of the section of the pipe, is below or above a certain value 
given by 

K/i/Dp, 

where I) is the diameter of the pipe, p the density of the water, and K a numerical 
constant, the value of which according to my experiments and, as I was able to show, 
to all the experiments by Poiseuille and Darcy, is for j>ipes of circular section 
between 

1900 and 2000, 

or, in other words, steady direct motion in round tubes is stable or unstable according 
as 



P 



<1900 or >2000, 



the number K being thus a criterion of the possible maintenance of sinuous or 
eddying motion. 

3. The experiments also showed that K was equally a criterion of the law of the 
resistance to be overcome — which changes from a resistance proportional to the 

* 'Phil. Trans.,' 1883, Part III., p. 935. 



. FLUIDS AND THE DETERMINATION OF THE CRITERION. 125 

velocity and in exact accordance with the theoretical results obtained from the 
singular solution of the equation, when direct motion changes to sinuous, i.e., when 

p = K. 

4. In the same paper I pointed out that the existence of this sudden change in the 
law of motion of fluids between solid surfaces when 

DU m = ^K 
p 

proved the dependence of the manner of motion of the fluid on a relation between 
the product of the dimensions of the pipe multiplied by the velocity of the fluid and 
the product of the molecular dimensions multiplied by the molecular velocities which 
determine the value of 

for the fluid, also that the equations of motion for viscous fluid contained evidence of 
this relation. 

These experimental results completely removed the discrepancy previously noticed, 
showing that, whatever may be the cause, in those cases in which the experimental 
results do not accord with those obtained by the singular solution of the equations, 
the actual motions of the water are different. But in this there is only a partial 
explanation, for there remains the mechanical or physical significance of the existence 
of the criterion to be explained. 

5. [My object in this paper is to show that the theoretical existence of an inferior 
limit to the criterion follows from the equations of motion as a consequence : — 

(1) Of a more l'igorous examination and definition of the geometrical basis on 
which the analytical method of distinguishing between molar-motions and heat- 
motions in the kinetic theory of matter is founded ; and 

(2) Of the application of the same method of analysis, thus definitely founded, to 
distinguish between mean-molar-motions and relative-molar-motions where, as in the 
case of steady-mean-flow along a pipe, the more rigorous definition of the geometrical 
basis shows the method to be strictly applicable, and in other cases where it is 
approximately applicable. 

The geometrical relation of the motions respectively indicated by the terms 
mean-molar-, or Mean-Mean-Motion, and relative-molar or Kelative-Mean-Motion 
being essentially the same as the relation of the respective motions indicated by the 
terms molar-, or Mean-Motion, and relative-, or Heat-Motion, as used in the theory 
of gases. 

I also show that the limit to the criterion obtained by this method of analysis and 
by integrating the equations of motion in space, appeal's as a geometrical limit to the 



126 PROFESSOR 0. REYNOLDS ON INCOMPRESSIBLE VISCOUS 

p>ossible simultaneous distribution of certain quantities in space, and in no wise 
depends on the physical significance of these quantities. Yet the physical significance 
of these quantities, as defined in the equations, becomes so clearly exposed as to 
indicate that further study of the equations would elucidate the properties of matter 
and mechanical principles involved, and so be the means of explaining what has 
hitherto been obscure in the connection between thermodynamics and the principles 
of mechanics. 

The geometrical basis of the method of analysis used in the kinetic theory of gases 
has hitherto consisted : — 

(1) Of the geometrical principle that the motion of any point of a mechanical 
system may, at any instant, be abstracted into the mean motion of the whole system 
at that instant, and the motion of the point relative to the mean-motion ; and 

(2) Of the assumption that the component, in any particular direction, of the 
velocity of a molecule may be abstracted into a mean-component-velocity (say u) 
which is the mean-component velocity of all the molecules in the immediate 
neighbourhood, and a relative velocity (say f), which is the difference between u 
and the component-velocity of the molecule ;* u and f being'so related that. M being 
the mass of the molecule, the integrals of (Mf ), and (M«£), &c, over all the molecules 
in the immediate neighbourhood are zero, and % [M (u + f ) 2 ] = % [M (u 2 + f 2 )].t 

The geometrical principle (l) has only been used to distinguish between the energy 
of the mean-motion of the molecule and the energy of its internal motions taken 
relatively to its mean motion ; and so to eliminate the internal motions from all 
further geometrical considerations which rest on the assumption (2). 

That this assumption (2) is purely geometrical, becomes at once obvious, when it is 
noticed that the argument relates solely to the distribution in space of certain 
quantities at a particular instant of time. And it appears that the questions as to 
whether the assumed distinctions are possible under any distributions, and, if so, 
under what distribution, are proper subjects for geometrical solution. 

On putting aside the apparent obviousness of the assumption (2), and considering 
definitely what it implies, the necessity for further definition at once appears. 

The mean component- velocity (w) of all the molecules in the immediate neighbour- 
hood of a point, say P, can only be the mean component- velocity of all the molecules in 
some space (S) enclosing P. u is then the mean-component velocity of the mechanical 
system enclosed in S, and, for this system, is the mean velocity at every point within 
S, and multiplied by the entire mass within S is the whole component momentum 
of the system. But,accordmg to the assumption (2), u with its derivatives are to be 
continuous functions of the position of P, which functions may vary from point to 
point even within S ; so that u is not taken to represent the mean component- velocity 
of the system within S, but the mean-velocity at the point P. Although there seems 
to have been no specific statement to that effect, it is presumable that the space S has 

* " Dynamical Theory of Gases," 'Phil. Trans.,' 1866, pp. 67. f ' Phil. Trans.,' 1866, p. 71. 



FLUIDS AND THE DETERMINATION OF THE CRITERION. 127 

been assumed to be so taken that P is the centre of gravity of the system within S. 
The relative positions of P and S being so defined, the shape and size of the space S 
requires to be further defined, so that u, &c, may vary continuously with the position 
of P, which is a condition that can always be satisfied if the size and shape of S may 
vary continuously with the position of P. 

Having thus defined the relation of P to S and the shape and size of the latter, 
expressions may be obtained for the conditions of distribution of u, for which 2 (M£) 
taken over S will be zero, i.e., for which the condition of mean-momentum shall be 
satisfied. 

Taking S l5 u x , &c, as relating to a point P x and S, u, &c, as relating to P, another 
point of which the component distances from P x are x, y. z, P 1 is the C.G. of S 1( and 
by however much or little S may overlap S ls S has its centre of gravity at x, y, z, 
and is so chosen that u, &c, may be continuous functions of x, y, z. it may, 
therefore, differ from u x even if P is within S x . Let u be taken for every molecule of 
the system S x . Then according to assumption (2), %QA_u) over S 2 must represent the 
component of momentum pf the system within S l9 that is, in order to satisfy the 
condition of mean momentum, the mean-value of the variable quantity u over the 
system S x must be equal to u Y the mean-component velocity of the system S 1( and 
this is a condition which in consequence the geometrical definition already mentioned 
can only be satisfied under certain distributions of u. For since u is a continuous 
function of re, y, z, M (u — u x ) may be expressed as a function of the derivatives of u at P x 
multiplied by corresponding powers and products of x, y, z, and again by M ; and by 
equating the integral of this function over the space S : to zero, a definite expression 
is obtained, in terms of the limits imposed on x, y, z, by the already defined space Sj 
for the geometrical condition as to the distribution of u under which the condition of 
mean momentum can be satisfied. 

From this definite expression it appears, as has been obvious all through the 
argument, that the condition is satisfied if u is constant. It also appears that there 
are certain other well-defined systems of distribution for which the condition is 
strictly satisfied, and that for all other distributions of u the condition of mean- 
momentum can only be approximately satisfied to a degree for which definite 
expressions appear. 

Having obtained the expression for the condition of distribution of u, so as to 
satisfy the condition of mean momentum, by means of the expression for M (u — u'), 
&c, expressions are obtained for the conditions as to the distribution of f, &c, in 
order that the integrals over the space S x of the products M (u£), &c. may be zero when 
% [M (u — u x )~\ = 0, and the conditions of mean energy satisfied as well as those of 
mean-momentum. It then appears that in some particular cases of distribution of u, 
under which the condition of mean momentum is strictly satisfied, certain conditions 
as to the distribution of £, &c, must be satisfied in order that the energies of mean- 



128 PROFESSOR 0. REYNOLDS ON INCOMPRESSIBLE VISCOUS 

and relative-motion may be distinct. These conditions as to the distribution of £ &c, 
are, however, obviously satisfied in the case of heat motion, and do not present 
themselves otherwise in this paper. 

From the definite geometrical basis thus obtained, and the definite expressions 
which follow for the condition of distribution of u, &c, under which the method of 
analysis is strictly applicable, it appears that this method may be rendered generally 
applicable to any system of motion by a slight adaptation of the meaning of the 
symbols, and that it does not necessitate the elimination of the internal motion of 
the molecules, as has been the custom in the theory of gases. 

Taking u, v, w to represent the motions (continuous or discontinuous) of the matter 

passing a point, and p to represent the density at the point, and putting u, &c, for 
the mean-motion (instead of u as above), and u', &c, for the relative-motion (instead 

of £ as before), the geometrical conditions as to the distribution of u, Sec, to satisfy 
the conditions of mean-momentum and mean-energy are, substituting p for M, of 
precisely the same form as before, and as thus expressed, the theorem is applicable to 
any mechanical system however abstract. 

(1) In order to obtain the conditions of distribution of molar-motion, under which 
the condition of mean-momentum will be satisfied so that the energy of molar-motion 
may be separated from that of the heat-motion, u, &c, and p are taken as referring to 
the actual motion and density at a point in a molecule, and S x is taken of such 
dimensions as may correspond to the scale, or periods in space, of the molecular 

distances, then the conditions of distribution of u, under which the condition of mean- 
momentum is satisfied, become the conditions as to the distribution of molar-motion, 
under which it is possible to distinguish between the energies of molar-motions and 
heat-motions. 

(2) And, when the conditions in (1) are satisfied to a sufficient degree of approxi- 
mation by taking u to l-epresent the molar-motion (u in (1)), and the dimensions of 
the space S to correspond with the period in space or scale of any possible periodic or 

eddying motion. The conditions as to the distribution of u, &c. (the components of 
mean-mean-motion), which satisfy the condition of mean-momentum, show the 
conditions of mean-molar-motion, under which it is possible to separate the energy 
of mean-molar-motion from the energy of relative-molar- (or relative-mean-) motion 

Having thus placed the analytical method used in the kinetic theory on a definite 
geometrical basis, and adapted so as to render it applicable to all systems of motion, 
by applying it to the dynamical theory of viscous fluid, I have been able to show : — ■ 
Feb. 18, 1895.] 

(a) That the adoption of the conclusion arrived at by Sir Gabriel Stokes, that the 
dissipation function represents the rate at which heat is produced, adds a definition 
to the meaning of u, v, to — the components of mean or fluid velocity — which was 
previously wanting ; 



FLUIDS AND THE DETERMINATION OP THE CRITERION. 129 

(b) That as the result of this definition the equations are true, and are only true 
as applied to fluid in which the mean-motions of the matter, excluding the heat- 
motions, are steady ; 

(o) That the evidence of the possible existence of such steady mean-motions, while 
at the same time the conversion of the energy of these mean-motions into heat is 
going on, proves the existence of some discriminative cause by which the periods in 
space and time of the mean-motion are prevented from approximating in magnitude 
to the corresponding periods of the heat-motions, and also proves the existence of 
some general action by which the energy of mean-motion is continually transformed 
into the energy of heat-motion without passing through any intermediate stage ; 

(d) That as applied to fluid in unsteady mean-motion (excluding the heat-motions), 
however steady the mean integral flow may be, the equations are approximately true 
in a degree which increases with the ratios of the magnitudes of the periods, in time 
and space, of the mean-motion to the magnitude of the corresponding periods of the 
heat-motions ; 

(e) That if the discriminative cause and the action of transformation are the result 
of general properties of matter, and not of properties which affect only the ultimate 
motions, there must exist evidence of similar actions as between the mean-mean- 
motion, in directions of mean flow, and the periodic mean-motions taken relative to 
the mean-mean-motion but excluding heat-motions. And that such evidence must be 
of a general and important kind, such as the unexplained laws of the resistance of 
fluid motions, the law of the universal dissipation of energy and the second law of 
thermodynamics ; 

(f) That the generality of the effects of the properties on which the action of trans- 
formation depends is proved by the fact that resistance, other than proportional to 
the velocity, is caused by the relative (eddying) mean-motion. 

(g) That the existence of the discriminative cause is directly proved by the 
existence of the criterion, the dependence of which on circumstances which limit the 
magnitudes of the periods of relative mean-motion, as compared with the heat-motion, 
also proves the generality of the effects of the properties on which it depends. 

(h) That the proof of the generality of the effects of the properties on which the 
discriminative cause, and the action of transformation depend, shows that — if in the 
equations of motion the mean-mean-motion is distinguished from the relative-mean- 
motion in the same way as the mean-motion is distinguished from the heat-motions — 
(1) the equations must contain expressions for the transformation of the energy of 
mean-mean-motion to energy of relative-mean-motion ; and (2) that the equations, 
when integrated over a complete system, must show that the possibility of relative- 
mean-motion depends on the ratio of the possible magnitudes of the periods of relative- 
mean-motion, as compared with the corresponding magnitude of the periods of the 
heat-motions. 

(i) That when the equations are transformed so as to distinguish between the 

MDCCCXCV. — A. S 



130 PROFESSOR 0. REYNOLDS ON INCOMPRESSIBLE VISCOUS 

mean-mean-motions, of infinite periods, and the relative-mean-motions of finite periods, 
there result two distinct systems of equations, one system for mean-mean-motion, as 
affected by relative-mean-motion and heat-motion, the other system for relative-mean- 
motion as affected by mean-mean-motion and heat-motions. 

{j) That the equation of energy of mean-mean-motion, as obtained from the first 
system, shows that the rate of increase of energy is diminished by conversion into 
heat, and by transformation of energy of mean-mean-motion in consequence of the 
relative-mean-motion, which transformation is expressed by a function identical in 
form with that which expresses the conversion into heat ; and that the equation of 
energy of relative-mean-motion, obtained from the second system, shows that this 
energy is increased only by transformation of energy from mean-mean-motion 
expressed by the same function, and diminished only by the conversion of energy 
of relative-mean-motion into heat. 

(k) That the difference of the two rates (l) transformation of energy of mean-mean- 
motion into energy of relative-mean-motion as expressed by the transformation 
function, (2) the conversion of energy of relative-mean-motion into heat, as expressed 
by the function expressing dissipation of the energy of relative-mean-motion, affords 
a discriminating equation as to the conditions under which relative-mean-motion 
can be maintained. 

(I) That this discriminating equation is independent of the energy of relative-mean - 
motion, and expresses a relation between variations of mean-mean-motion of the first 
order, the space periods of relative-mean-motion and \i\p such that any circumstances 
which determine the maximum periods of the relative-mean-motion determine the 
conditions of mean-mean-motion under which relative mean-motion will be maintained 
— determine the criterion. 

(in) That as applied to water in steady mean flow between parallel plane surfaces, 
the boundary conditions and the equation of continuity impose limits to the maximum 
space periods of relative-mean-motion such that the discriminating equation affords 
definite proof that when an indefinitely small sinuous or relative disturbance exists 
it must fade away if 

pDXJJ/j, 

is less than a certain number, which depends on the shape of the section of the 
boundaries, and is constant as long as there is geometrical similarity. While for 
greater values of this function, in so far as the discriminating equation shows, the 
energy of sinuous motion may increase until it reaches to a definite limit, and rules 
the resistance. 

(n) That besides thus affording a mechanical explanation of the existence of the 
criterion K, the discriminating equation shows the purely geometrical circumstances 
on which the value of K depends, and although these circumstances must satisfy 
geometrical conditions required for steady mean-motion other than those imposed by 



FLUIDS AND THE DETERMINATION OP THE CRITERION. 



131 



the conservations of mean energy and momentum, the theory admits of the determi- 
nation of an inferior limit to the value of K under any definite boundary conditions, 
which, as determined for the particular case, is 

517. 

This is below the experimental value for round pipes, and is about half what might 
be expected to be the experimental value for a flat pipe, which leaves a margin to meet 
the other kinematical conditions for steady mean-mean-motion. 

(o) That the discriminating equation also affords a definite expression for the 
resistance, which proves that, with smooth fixed boundaries, the conditions of 
dynamical similarity under any geometrical similar circumstances depend only on the 
value of 

fjr dx 

where b is one of the lateral dimensions of the pipe ; and that the expression for this 
resistance is complex, but shows that above the critical velocity the relative-mean- 
motion is limited, and that the resistances increase as a power of the velocity higher 
than the first. 

Section II. 

The Mean-motion and Heat-motions as distinguished by Periods. — Mean-mean- 
motion and Relative-mean-motion. — Discriminative Cause and Action of Trans- 
formation. — Two Systems of Equations. — A Discriminating Equation. 

6. Taking the general equations of motion for incompressible fluid, subject to no 
external forces to be expressed by 



- ji (P** + P uu ) + J-y (?V + puv) + -yjr \ (•" "' I 



clt 
dv 



dx 

d_ 
dx 



dz 



{Pzy + pvu) + ~ {Vyy + P vv ) + ^ (P*y + P vw ) ] > 

p Tt = ~ Ydx &~ + p wu ) + % (p* + pwv "> + & (-?» + P"™)} 



0). 



with the equation of continuity 

= clu/dx + dv/dy + divjdz 



(2), 



where p xx , &c, are arbitrary expressions for the component forces per unit of area, 
resulting from the stresses, acting on the negative faces of planes perpendicular to 



s 2 



132 



PROFESSOR 0. REYNOLDS ON INCOMPRESSIBLE VISCOUS 



the direction indicated by the first suffix, in the direction indicated by the second 
suffix. 

Then multiplying these equations respectively by u, v, iv, integrating by parts, 
adding and putting 

2E for p (u 2 + v° + iv 2 ) 

and transposing, the rate of increase of kinetic energy per unit of volume is given by 



d d d , d * 



T, ( U P**) + Ty foP*-) + i ^ 



dx 

d 

dt 

d 
dx 



J -j:A v P^) + ^(«3>») + ' i r i> ' ' 



^W + ^WH / 



dz 
d_ 
dz 

A 
dz 



du du du 



dx 



dv dv dv 



dw dw , div 



dy 

dv 

dw 
dy 



(3). 



The left member of this equation expresses the rate of increase in the kinetic 
energy of the fluid per unit of volume at a point moving with the fluid. 

The first term on the right expresses the rate at which work is being done by the 
surrounding fluid per unit of volume at a point. 

The second term on the right therefore, by the law of conservation of energy, 
expresses the difference between the rate of increase of kinetic energy and the rate 
at which work is being done by the stresses. This difference has, so far as I am 
aware, in the absence of other forces, or any changes of potential energy, been equated 
to the rate at which heat is being converted into energy of motion, Sir Gabriel 
Stokes having first indicated this* as resulting from the law of conservation of 
energy then just established by Joule. 

7. This conclusion, that the second term on the right of (3) expresses the rate at 
which heat is being converted, as it is usually accepted, may be correct enough, but 
there is a consequence of adopting this conclusion which enters largely into the 
method of reasoning in this paper, but which, so far as I know, has not previously 
received any definite notice. 



; Cambridge Phil. Trans.,' vol. 9, p. 57. 



FLUIDS AND THE DETERMINATION OF THE CRITERION. 133 

TJie Component Velocities in the Equations of Viscous Fluids. 

In no case, that I am aware of, has any very strict definition of u, v, iv, as they 
occur in. the equations of motion, been attempted. They are usually defined as the 
velocities of a particle at a point (x, y, z) of the fluid, which may mean that they are 
the actual component velocities of the point in the matter passing at the instant, or 
that they are the mean velocities of all the matter in some space enclosing the point, 
or which passes the point in an interval of time. If the first view is taken, then the 
right hand member of the equation represents the rate of increase of kinetic energy, 
per unit of volume, in the matter at the point ; and the integral of this expression 
over any finite space S, moving with the fluid, represents the total rate of increase 
of kinetic energy, including heat-motion, within that space ; hence the difference 
between the rate at which work is done on the surface of S, and the rate at which 
kinetic energy is increasing can, by the law of conservation of energy, only represent 
the rate at which that part of the heat which does not consist in kinetic energy of 
matter is being produced, whence it follows : — ■ 

(«) That the adoption of the conclusion that the second term in equation (3) ex- 
presses the rate at which heat is being converted, defines u, v, w, as not representing 
the component velocities of points in the passing matter. 

Further, if it is understood that u, v, w, represent the mean velocities of the matter 
in some space, enclosing x, y, z, the point considered, or the mean velocities at a point 
taken over a cei"tain interval of time, so that % (pu), 2 (pv), 2 (piv) may express the 
components of momentum, and zl, (pv) — yl(pw), &c, &c, may express the com- 
ponents of moments of momentum, of the matter over which the mean is taken ; 
there still remains the question as to what spaces and what intervals of time ? 

(6) Hence the conclusion that the second term expresses the rate of conversion of heat, 
defines the spaces and intervals of time over which the mean component velocities must 
be taken, so that E may include all the energy of mean-motion, and exclude that of 
heat-motions. 

Equations Approximate only except in Three Particular Cases. 

8. According to the reasoning of the last article, if the second term on the right of 
equation (3) expresses the rate at which heat is being converted into energy of mean- 
motion, either pu, pv, pw express the mean components of momentum of the matter, 
taken at any instant over a space S enclosing the point x, y, z, to which u, v, w 
refer, so that this point is the centre of gravity of the matter within S and such 
that p represents the mean density of the matter within this space ; or pu, pv, piv 
represent the mean components of momentum taken at x, y, z over an interval of time t, 
such that p is the mean density over the time r, and if t marks the instant to which 
u, v, w refer, and t' any other instant, X[(t — t') p\, in which p is the actual density, 
taken over the interval t is zero. The equations, however, require, that so obtained, 



134 PROFESSOR 0. REYNOLDS ON INCOMPRESSIBLE VISCOUS 

p, u, v, w, shall be continuous functions of space and time, and it can be shown that 
this involves certain conditions between the distribution of the mean-motion and the 
dimensions of S and r. 

Mean- and Relative-Motions of Matter. 

Whatever the motions of matter within a fixed space S may be at any instant, if 
the component velocities at a point are expressed by u, v, w, the mean component 
velocities taken over S will be expressed by 

5 = ^,&c. f 4o (4). 

If then u, v, w, are taken at each instant as the velocities of x, y, z, the instantaneous 
centre of gravity of the matter tvithin S, the component momentum at the centre of 
gravity may be put 

pu = pu + pu (5), 

where u is the motion of the matter, relative to axes moving with the mean velocity, 
at the centre of gravity of the matter within S. Since a space S of definite size and 
shape may be taken about any point x, y, z in an indefinitely larger space, so that 
x, y, z is the centre of gravity of the matter within S, the motion in the larger space 

may be divided into two distinct systems of motion, of which u, v, w represent a 
mean-motion at each point and u', v, 10 a motion at the same point relative to the 
mean -motion at the point. 

If, however, u, v, iv are to represeut the real mean-motion, it is necessary that 
S {pv'), 2 (/>u')j 2 (po)') summed over the space S, taken about any point, shall be 
severally zero ; and in order that this may be so, certain conditions must be fulfilled. 

For taking x, y, z for G the centre of gravity of the matter within S and x', y', z 
for any other point within S, and putting a, b, a for the dimensions of S in 

directions x, y, z, measured from the point x, y, z, since u, v, %v are continuous functions 
of x, y, z, by shifting S so that the centre of gravity of the matter within it is at 

x , y', z, the value of u for this point is given by 

i-%+c-)®,+to'-»)(f,+f-»(D,+t(^-J'®,+ te w 

where all the differential coefficients on the left refer to the point x, y, z ; and in the 
same way for v and 10. 

Subtracting the value of u thus obtained for the point x, y', z from that of u at the 



FLUIDS AND THE DETERMINATION OF THE CRITERION. 



135 



same point the difference is the value of u' at this point, whence svimming these 
differences over the space S about G at x, y, z, since by definition when summed over 
the space S about G 



2 [p (u — u ff )~\ = and 2 [p (x — as)] = 



(7) 



2 (pu) = -kt[p(x- x'f] (g) + i 2 [p (y-y'f] (' 



/'cPu\ 



\ d f')a 



dhi 



That is 



+ i t[p(z-z'f}{^ +&c. j,. (8a) . 



S(pn'). 



2 00 






^(-ri) +77I-J +-,hr +&C. 



In the same way if 2 ( ) be taken over the interval of time t including £ ; and 

for the instant £ 

2(pw) , - , 

m = _ V., , and p?^ = p« -f- pw ; 

then since for any other instant t' 



S=*+«-0 (§),+ l«-*T(f), + &o., 



where 2 [p (Z — «')] = 0, and 2 [p («< — u)] = 0. 
It appears that 



S( P «')=-2[ip(;-0 2 ]S + &c. J 



^ 2 



^- } is<-K(^,- - 



/cPu 



^ 



(8b). 



From equations (8a) and (8b), and similar equations for 2 (pv) and 2 (p« ; '), it appears 
that if 

2 (pu') = 2 (pv') = 2 (p«0 = 0, 



where the summation extends both over the space S and the interval t, all the terms 
on the right of equations (8a) and (8b) must be respectively and continuously zero, or, 

what is the same thing, all the differential coefficients of u, v, iv with respect to 
x, y, z and t of the first order must be respectively constant. 

This condition will be satisfied if the mean-motion is steady, or uniformly varying 



136 PROFESSOR 0. REYNOLDS ON INCOMPRESSIBLE VISCOUS 

with the time, and is everywhere in the same direction, being subject to no variations 
in the direction of motion ; for suppose the direction of motion to be that of x, then 
since the periodic motion passes through a complete period within the distance 2a, 
2 (pu) will be zero within the space 

2a dy dz, 

however small dy dz may be, and since the only vaiiations of the mean-motion are in 
directions y and z, in which b and c may be taken zero, and du/dt is everywhere 
constant, the conditions are perfectly satisfied. 

The conditions are also satisfied if the mean-motion is that of uniform expansion or 
contraction, or is that of a rigid body. 

These three cases, in which it may be noticed that variations of mean-motion 
are everywhere uniform in the direction of motion, and subject to steady variations 
in respect of time, are the only cases in which the conditions (8a), (8b), can be perfectly 
satisfied. 

The conditions will, however, be approximately satisfied, when the variations of 

u, v, w of the first order are approximately constant over the space S. 

In such case the right-hand members of equations (8a), (8b), are neglected, and it 
appears that the closeness of the approximations will be measured by the relative 
magnitude of such terms as 



"&* 



a d 2 u/dx 2 , &c, t dhijdt 2 as compared with du/dx, dujdt, &c. 

Since frequent reference must be made to these relative values, and, as in periodic 
motion, the relative values of such terms are measured by the period (in space or time) 
as compared with a, b, c and r, which are, in a sense, the periods of u, v , iv, I shall 
use the term period in this sense, taking note of the fact that when the mean-motion 
is constant in the direction of motion, or vaiies uniformly in respect of time, it is not 
periodic, i.e., its periods are infinite. 

9. It is thus seen that the closeness of the approximation with which the motion of 
any system can be expressed as a varying mean-motion together with a relative- 
motion, which, when integrated over a space of which the dimensions are a, b, c, has 

no momentum, increases as the magnitude of the periods of u, v, w in comparison with 
the periods of u, v', iv , and is measured by the ratio of the relative orders of magni- 
tudes to which these periods belong. 



Heat-motions in Matter are Approximately Relative to the Mean-motions. 

The general experience that heat in no way affects the momentum of matter, shows 
that the heat-motions are relative to the mean-motions of matter taken over spaces of 



FLUIDS AND THE DETERMINATION OF THE CRITERION. 137 

sensible size. But, as heat is by no means the only state of relative-motion of matter, 
if the heat-motions are relative to all mean-motions of matter, whatsoever their periods 
may be, it follows — that there must be some discriminative cause which prevents the 
existence of relative-motions of matter other than heat, except mean-motions with 
periods in time and space of greatly higher orders of magnitude than the corres- 
ponding periods of the heat-motions — otherwise, by equations (8a), (8b), heat-motions 
could not be to a high degree of approximation relative to all other motions, and we 
could not have to a high degree of approximation, 

du , du dit, 

dv dv dv 

P*,T- + Pwj; + P«,^->=-ir(pH) (9), 



dx ** dy 

dw 
ly 



die dw dw 



where the expression on the right stands for the rate at which heat is converted into 
energy of mean-motion. 

Transformation of Energy of Relative-mean-motion to Energy of Heat-motion. 

10. The recognition of the existence of a discriminative cause, which prevents the 
existence of relative-mean-motions with periods of the same order of magnitude as 
heat-motions, proves the existence of another general action by which the energy of 
relative-mean-motion, of which the periods are of another and higher order of 
magnitude than those of the heat-motions, is transformed to energy of heat-motion. 

For if relative-mean-motions cannot exist with periods approximating to those of 
heat, the conversion of energy of mean-motion into energy of heat, proved by Joule, 
cannot proceed by the gradual degradation of the periods of mean-motion until these 
periods coincide with those of heat, but must, in its final stages, at all events, be the 
result of some action which causes the energy of relative-mean-motion to be trans- 
formed into the energy of heat-motions without intermediate existence in states of 
relative-motion with intermediate and gradually diminishing periods. 

That such change of energy of mean-motion to energy of heat may be properly 
called transformation becomes apparent when it is remembered that neither mean- 
motion nor relative- motion have any separate existence, but are only abstract 
quantities, determined by the particular process of abstraction, and so changes in the 
actual-motion may, by the process of abstraction, cause transformation of the 
abstract energy of the one abstract-motion, to abstract energy of the other abstract- 
motion. 

All such transformation must depend on the changes in the actual-motions, and so 

MDCCCXCV. — A. T 



138 PROFESSOR 0. REYNOLDS ON INCOMPRESSIBLE VISCOUS 

must depend on mechanical principles and the properties of matter, and hence the 
direct passage of energy of relative-mean-motion to energy of heat -motions is evidence 
of a general cause of the condition of actual-motion which results in transformation — 
which may be called the cause of transformation. 



The Discriminative Cause, and the Cause of Transformation. 

11. The only known characteristic of heat-motions, besides that of being relative 
to the mean-motion, already mentioned, is that the motions of matter which result 
from heat are an ultimate form of motion which does not alter so long as the mean- 
motion is uniform over the space, and so long as no change of state occurs in the 
matter. In respect of this characteristic, heat-motions are, so far as we know, 
unique, and it would appear that heat-motions are distinguished from the mean- 
motions by some ultimate properties of matter. 

It does not, however, follow that the cause of transformation, or even the 
discriminative cause, are determined by these properties. Whether this is so or not 
can only be ascertained by experience. If either or both these causes depend solely 
on properties of matter which only affect the heat-motions, then no similar effect 
would result as between the variations of mean-mean-motion and relative-mean- 
motion, whatever might be the difference in magnitude of their respective periods. 
Whereas, if these causes depend on properties of matter which affect all modes of 
motion, distinctions in periods must exist between mean-mean-motion and relative- 
mean-motion, and transformation of energy take place from one to the other, as 
between the mean-motion and the heat-motions. 

The mean-mean-motion cannot, however, under any circumstances stand to the 
relative-mean-motion in the same relation as the mean-motion stands to the heat- 
motions, because the heat-motions cannot be absent, and in addition to any trans- 
formation from mean-mean-motion to relative-mean-motion, there are transformations 
both from mean- and relative-mean-motion to heat-motions, which transformation 
may have important effects on both the transformation of energy from mean- to 
relative-mean-motion, and on the discriminative cause of distinction in their periods. 

In spite of the confusing effect of the ever present heat-motions, it would, however, 
seem that evidence as to the character of the properties on which the cause of trans- 
formation and the discriminative cause depend should be forthcoming as the result of 
observing the mean- and relative-mean-motions of matter. 

12. To prove by experimental evidence that the effects of these properties of 
matter are confined to the heat-motions, would be to prove a negative ; but if these 
properties are in any degree common to all modes of matter, then at first sight it 
must seem in the highest degree improbable that the effects of these causes on the 
mean- and relative-mean-motions would be obscure, and only to be observed by 
delicate tests. For pi^operties which can cause distinctions between the mean- and 



FLUIDS AND THE DETERMINATION OF THE CRITERION. 139 

heat-motions of matter so fundamental and general, that from the time these motions 
were first recognized the distinction has been accepted as part of the order of nature, 
and has been so familiar to us that its cause has excited no curiosity, cannot, if they 
have any effect at all, but cause effects which are general and important on the 
mean-motions of matter. It would thus seem that evidence of the general effects of 
such properties should be sought in those laws and phenomena known to us as the 
result of experience, but of which no rational explanation has hitherto been found ; 
such as the law that the resistance of fluids moving between solid surfaces and of 
solids moving through fluids, in such a manner that the general-motion is not 
periodic, is as the square of the velocities, the evidence covered by the law of the 
universal tendency of all energy to dissipation and the second law of thermo- 
dynamics. 

13. In considering the first of the instances mentioned, it will be seen that the 
evidence it affords as to the general effect of the properties, on which depends transforma- 
tion of energy from mean- to relative-motion, is very direct. For, since my experiments 
with colour bands have shown that when the resistance of fluids, in steady mean flow, 
vaiies with a power of the velocity higher than the first the fluid is always in a state 
of sinuous motion, it appears that the prevalence of such resistance is evidence of the 
existence of a general action by which energy of mean-mean-motion with infinite 
periods is directly transformed to the energy of relative-mean-motion, with finite 
periods, represented by the eddying motion, which renders the general mean-motion 
sinuous, by which transformation the state of eddying-motion is maintained, not- 
withstanding the continual transformation of its energy into heat-motions. 

We have thus direct evidence that properties of matter which determine the cause 
of transformation, produce general and important effects which are not confined to the 
heat-motions. 

In the same way, the experimental demonstration I was able to obtain, that 
relative-mean-motion in the form of eddies of finite peiiods, both as shown by colour 
bands and as shown by the law of resistances, cannot be maintained except under 
circumstances depending on the conditions which determine the superior limits to the 
velocity of the mean-mean-motion, of infinite periods, and the periods of the relative- 
mean-motion, as defined in the criterion 

DU^ = K, 

is not only a direct experimental proof of the existence of a discriminative cause which 
prevents the maintenance of periodic mean-motion except with periods greatly in excess 
of the periods of the heat-motions, but also indicates that the discriminative cause 
depends on properties of matter which affect the mean-motions as well as the heat- 
motions. 



T '1 



140 PROFESSOR 0. REYNOLDS ON INCOMPRESSIBLE VISCOUS 



Expressions for the Rate of Transformation and the Discriminative Cause. 

14. It has already been shown (Art. 8) that the equations of motion approximate 
to a true expression of the relations between the mean -motions and stresses, when the 
ratio of the periods of mean-motions to the periods of the heat-motions approximates 
to infinity. Hence it follows that these equations must of necessity include whatever 
mechanical or kinematical principles are involved in the transformation of energy of 
mean-mean-motion to energy of relative-mean-motion. It has also been shown that 
the properties of matter on which depends the transformation of energy of varying 
mean-motion to relative-motion are common to the relative-mean- motion as well as to 
the heat-motion. Hence, if the equations of motion are applied to a condition in 
which the mean-motion consists of two components, the one component being a mean- 
mean-motion, as obtained by integrating the mean-motion over spaces S x taken about 
the point x, y, z, as centre of gravity, and the other component being a relative-mean- 
motion, of which the mean components of momentum taken over the space S x every- 
where vanish, it follows : — 

(1) That the resulting equations of motion must contain an expression for the rate 
of transformation from energy of mean-mean-motion to energy of relative-mean- 
motion, as well as the expressions for the transformation of the respective energies of 
mean- and relative-mean-motion to energy of heat-motion ; 

(2) That, when integrated over a complete system these equations must shoiv that the 
possihility of the maintenance of the energy of relative-mean-motion depends, whatsoever 
may he the conditions, on the possible order of magnitudes of the periods of the relative- 
mean-motion, as compared with the periods of the heat-motions. 



The Equations of Mean- and Relative Mean-Motion. 

15. These last conclusions, besides bringing the general results of the previous 
argument to the test point, suggest the manner of adaptation of the equations 
of motion, by which the test may be applied. 

Put 

u = u + v', v = v + v, w = w + w' (11), 

where 

u = S(pu)/t(p), &c, &c (12), 

the summation extending over the space S x of which the centre of gravity is at the 



FLUIDS AND THE DETERMINATION OP THE CRITERION. 141 

point x, y, z. Then since u, v, to are continuous functions of x, y, z, therefore 

u, v, w, and u', v, w, are continuous functions of x, y, z. And as p is assumed 
constant, the equations of continuity for the two systems of motion are : 



du dv dw _ , 

dx dx dx 



du' dv' dv/ 
dx Ay ' dz 



(13); 



also both systems of motions must satisfy the boundary conditions, whatever they 
may be. 

Further putting p^, &c, for the mean values of the stresses taken over the space 
S x and 

l p' X x=Px X — pZ (14) 

and defining S : to be such that the space variations of u, v, w are approximately 

constant over this space, we have, putting u'u', &c, for the mean values of the squares 
and products of the components of relative-mean-motion, for the equations of mean- 
mean-motion, 



du 



PJt = 



&c. = 
&c. = 



= -{£&** 



+ pUU + pll'tl) + 7" {Pyx + PUV + pu'v ') 



+ J z (P-.* + put" + pu'io) 



&c. 
&c. 



(15), 



which equations are approximately true at every point in the same sense as that in 
which the equations (l) of mean-motion are true. 

Subtracting these equations of mean-mean-motion from the equations of mean- 
motion, we have 



d_ 

dx 



du' 



{p ' xx + P (UU + u'll) + p {ll'u' — U'u')} 



PjT=~ 1 + T iP'y* + P i uv ' + u ' v ) + P i u ' v ' ~ u ' v ')) \ &c - &c - ( 16 )' 



dt 



dy 
+ j- {p' Z x + p (uiv' + u'w) + p {u'w — u'w) \ 



which are the equations of momentum of relative-mean-motion at each point. 



142 



PROFESSOR 0. REYNOLDS ON INCOMPRESSIBLE VISCOUS 



Again, multiplying the equations of mean-mean-motion by u, v, w respectively, 
adding and putting 2E = p (u 2 + v 2 + w*), we obtain ; 



d - d - d — • d\ = 
at dx dy dzj 



T» O (P~ + »V)3 + J O (ft> + **«■')■] + ^O (2?« + w '^')] 






«Z r- ,- 



<Z -- ,- 



+ ^ 1> (p*/ + vV ) ] + ^ Ca» .+ vV ) ].+. %b (p» + ^ ) ] > 



\ < + dxl w (p*:+ w ' u 'fi + f ^l>~(zv+™ v )] -f t„[. w (p°*+ w ' w ')] 



dz 



— du — du , — die 



——-7 tfc — t—^ <?W , —7 — , tfoi 

MM — + U V \- UIO — 

dx dy dz 



\) - — dv , — dv , ■— c?i' i _j_ -j - —;-- dv , —,—rdv 
+ 1 + **£ + ***+***; y + * + VU I.+ VV d V + V 



dy 



dy 



dw , dw — dvj 

dy "*" ^" dz~ 



+ P**^ + P^+P* 



dy 



W- \ (17) 

dz 



—r-, dw —,-, dw —i—, dw 

+ W U — + W V hlOW — 

dx dy dz 



which is the approximate equation of energy of mean-mean-motion in the same sense 
as the equation (3) of energy of mean-motion is approximate. 

In a similar manner multiplying the equations (16) for the momentum of relative- 
mean -motion respectively by u, v', w, and adding, the result would be the equation 
for energy of relative-mean-motion at a point, but this would include terms of 
which the mean values taken over the space Si are zero, and, since all corresponding 
terms in the energy of heat are excluded, by summation over the space S in the 
expression for the rate at which mean-motion is transformed into heat, there is no 
reason to include them for the space Si ; so that, omitting all such terms and putting 



2E' = p {u 3 + v* + w'*) 



(18), 



we obtain 



FLUIDS AND THE DETERMINATION OF THE CRITERION. 



143 



(!+^+^+«IV 



(Lv dy 

d_ 
dx 

A 

dx 

d_ 

dx 



fa 
^ [u (p'.„ + pw'u'J] + - [«' (pV, + mV)] + ^ 0' (p' y , + «V)] 

- 4 + £ [>' (p'y* + «V)] + I K My* + «V)] + | [>' (^ + «V)J j- 



- t, IV (p» + W, ' M ')] + ^ K te'** + wV )] + i K (p« + wV )] 



-I 
dz 1 



, du' , du' , dvl 



dx 



dz 



/ ! 



"* <fc +P ^ dy ^ P: * dz I 
, dv/ , , dw' , , «&«' 



—7—7 C?it —7—7- C?M —t 7 dl(, 

pun rx + P uv Ty + puw- 

-,— r dv -r-r dv -7—7 rfiJ 

+ pvu s + /w« ^ + /»«* 



-j—>dio 



dw 



+ p?r « — + p«Ci) - — I- pw> „„ 
r (to r dy r dz 



'■ - — H aw w 



ki9) 



where only the mean values, over the space S^ of the expressions in the right member 
are taken into account. 

This is the equation for the mean rate, over the space S,, of change in the energy 
of relative-mean-motion per unit of volume. 

It may be noticed that the rate of change in the energy of mean-mean-motion, 
together with the mean rate of change in the energy of relative-mean-motion, must 
be the total mean-rate of change in the energy of mean-motion, and that by adding 
the equations (17) and (19) the result is the same as is obtained from the equation (3) 
of energy of mean-motion by omitting all terms which have no mean value as summed 
over the space Sj. 

The Expressions from Transformation of Energy from Mean-mean-motion to Relative' 

mean-motion. 



16. When equations (17) and (19) are added together, the only expressions that 
do not appear in the equation of mean energy of mean-motion are the last terms on 
the right of each of the equations, which are identical in form and opposite in sign. 

These terms which thus represent no change in the total energy of mean-motion 
can only represent a transformation from energy of mean-mean-motion to energy of 
relative-mean-motion. And as they are the only expressions which do not form part 
of the general expression for the rate of change of the mean energy of mean-motion, 
they represent the total exchange of energy between the mean-mean-motion and the 
relative-mean-motion . 

It is also seen that the action, of which these terms express the effect, is purely 



144 PROFESSOR O. REYNOLDS ON INCOMPRESSIBLE VISCOUS 

kinematical, depending simply on the instantaneous characters of the mean- and 
relative-mean-motion, whatever may be the properties of the matter involved, or the 
mechanical actions which have taken part in determining these characters. The 
terms, therefore, express the entire result of transformation from energy of mean- 
mean-motion to energy of relative-mean-motion, and of nothing but the transforma- 
tion. Their existence thus completely verifies the first of the general conclusions 
in Art. 14. 

The term last but one in the right member of the equation (17) for energy of 
mean-mean-motion expresses the rate of transformation of energy of heat-motions 
to that of energy of mean-mean-motion, and is entirely independent of the relative- 
mean-motion. 

In the same way, the term last but one on the right of the equation (19) for 
energy of relative-mean-motion expresses the rate of transformation from energy of 
heat-motions to energy of relative-mean-motion, and is quite independent of the 
mean -mean-motion . 

17. In both equations (17) and (19) the first terms on the right express the rates 
at which the respective energy of mean- and relative-mean-motion are increasing 
on account of work done by the stresses on the mean- and relative-motion 
respectively, and by the additions of momentum caused by convections of relative- 
mean-motion by relative-mean-motion to the mean- and relative-mean-motions 
respectively. 

It may also be noticed that while the first term on the right in the equation (19) 
of energy of relative-mean-motion is independent of mean-mean-motion, the corre- 
sponding term in equation (17) for mean-mean-motion is not independent of relative- 
mean-motion. 

A Discriminating Eqtiation. 

18. In integrating the equations over a space moving with the mean-mean-motion 
of the fluid the first terms on the right may be expressed as surface integrals, which 
integrals respectively express the rates at which work is being done on, and energy 
is being received across, the surface by the mean-mean-motion, and by the relative- 
mean-motion. 

If the space over which the integration extends includes the whole system, or such 
part that the total energy conveyed across the surface by the relative-mean-motion is 
zero, then the rate of change in the total energy of relative-mean-motion within the 
space is the difference of the integral, over the space, of the rate of increase of this 
energy by transformation from energy of mean-mean-motion, less the integral rate 
at which energy of relative-mean-motion is being converted into heat, or integrating 
equation (19), 



FLUIDS AND THE DETERMINATION OF THE CRITERION. 



145 



m 



- d 



d\ 



-\- v -f- - w -j- 1 E' dx dy dz = 
dt ' dx dy ' dz) J 



—,—f du —f—r du — — , du ~*\ 

puu — + p u v -r + pu w ~r ! 
dx r dy dz ; 

7 ~(h j 



dv 



-— dv 



- pv'% f- pv'v — -f pv'w 



I 



dx 

dw 
dx 



dz 



> dx dy dz 



—;—, dw -7-7 dw , —7 — , dw 

\-pwu Vpwv — +pww — 



f w — 

dx 



, dv! ' 



+ Jff<* 



(ft/ , */ 

^y .7„, i V yy 



dv 



dx 



dy 

dw' 



+ p' zl/ — y dx dy dz 



, dw' , 

P*^+P»'-dJ + P'-d, 



d; 

div' 



(20). 



This equation expresses the fundamental relations : — 

(1) That the only integral effect of the mean-mean-motion on the relative-mean- 
motion is the integral of the rate of transformation from energy of mean-mean- 
motion to energy of relative-mean-motion. 

(2) That, unless relative energy is altered by actions across the surface within which 
the integration extends t the integral energy of relative-mean-motion will be increasing 
or diminishing according as the integral rate of transformation from mean-mean- 
motion to relative-mean-motion is greater or less than the rate of conversion of the 
energy of relative-mean-motion into heat. 

19. For p'zx, &c, are substituted their values as determined according to the 
theory of viscosity, the approximate truth of which has been verified, as already 
explained. 

Putting 

du 



, , /du' dv' , dw'\ 

(dv! dv'\ 



y 



(21), 



we have, substituting in the last term of equation (20), as the expression for the 
rate of conversion of energy of relative-mean-motion into heat, 



-fffi(pH)*4r*-fff 



/du' dv' dw' 
^ > \dx + 'dy"^ ~- 



dz 



hi! 



, dv' , dv/'v 1 
^chj+Tz) + 2 



du'V fdv'Y . (duTf] 



MDCCCXCV. — A. 



+(S+f)*+(£+3 ,+ (s+¥?}]***- ■ w 

u 



146 PROFESSOR O. REYNOLDS ON INCOMPRESSIBLE VISCOUS 

in which /x is a function of temperature only ; or since p is here considered as constant, 

d 



it 



pH' = ■- p. 



*^V_L !^Y-L (—""' 

dx) + \di/J + Yds 






+ fj+(f + £)"> 



dz 



■ (23), 



whence substituting for the last term in equation (20) we have, if the energy of 
relative-mean-motion is maintained, neither increasing or diminishing, 



-P 



—;—, dll , —7—7- dU , — 7— t- OM 

It It -: r- W V — + u w T 

dx ay dz 



dv 



7—7- dv — , — 7 dv 



+ v u - — |- v v' — + w w' 



cfe 



rfy 



<fe 



_ 7 _ > dw —7-7 ffoO —7—7 Cfrtf 

+ W W \- WV — -f- V)W — ' 

fl.v ay aa 



> da; dy dz 



-4\ 



c I!!l\" i /^A 2 i /*^ 



aa 



U/ 



T 



+ \ (/y + dz ) + \ dz + <& 



> cfo cZy c?z = 



(24), 



which is a discriminating equation as to the conditions under which relative-mean- 
motion can be sustained. 

20. Since this equation is homogeneous in respect to the component velocities of 
the relative-mean-motion, it at once appears that it is independent of the energy of 
relative-mean-motion divided by the p. So that if p,/p is constant, the condition it 
expresses depends only on the relation between variations of the mean-mean-motion 
and the directional, or angular, distribution of the relative-mean-motion, and on the 
squares and products of the space periods of the relative-mean- motion. 

And since the second term expressing the rate of conversion of heat into energy of 
relative-mean-motion is always negative, it is seen at once that, whatsoever may be 
the distribution and angular distribution of the relative-mean-motion and the varia- 
tions of the mean-mean-motion, this equation must give an inferior limit for the rates 
of variation of the components of mean-mean-motion, in terms of the limits to the 
periods of relative-mean-motion, and p./p, within which the maintenance of relative- 
mean-motion is impossible. And that, so long as the limits to the periods of relative- 
mean-motion are not infinite, this inferior limit to the rates of variation of the mean- 
mean-motion will be greater than zero. 



FLUIDS AND THE DETERMINATION OF THE CRITERION. 1±7 

Thus the second conclusion of Art. 14, and the whole of the previous argument is 
verified, and the properties of matter which prevent the maintenance of mean-motion 
with periods of the same order of magnitude as those of the heat-motion are shown to 
be amongst those properties of matter which are included in the equations of motion 
of which the truth has been verified by experience. 



The Cause of Transformation. 

21. The transformation function, which appears in the equations of mean-energy of 
mean- and relative-mean-motion, does not indicate the cause of transformation, but 
only expresses a kinematical principle as to the effect of the variations of mean-meau- 
motion, and the distribution of relative-mean-motion. In order to determine the 
properties of matter and the mechanical principles on which the effect of the variations 
of the mean-mean-motion on the distribution and angular distribution of relative-mean- 
motion depends, it is necessary to go back to the equations (16) of relative-momentum 
at a point ; and even then the cause is only to be found by considering the effects of 
the actions which these equations express in detail. The determination of this cause, 
though it in no way affects the proofs of the existence of the criterion as deduced from 
the equations, may be the means of explaining what has been hitherto obscure in the 
connection between thermodynamics and the principles of mechanics. That such may 
be the case, is suggested by the recognition of the separate equations of mean- and 
relative -mean-motion of matter. 

Tlie Equation of Energy of Relative-mean- motion and the Equation of 

Thermodynamics. 

22. On consideration, it will at once be seen that there is more than an accidental 
correspondence between the equations of energy of mean- and relative-rnean-motion 
respectively and the respective equations of energy of mean-motion and of heat in 
thermodynamics. 

If instead of including only the effects of the heat-motion on the mean-momentum 
as expressed by p xx , &c, the effects of relative-mean-motion are also included by 

putting p IX for p xx + pu'u, &c, and fy: f° r Vy» + pw'v', &c, in equations (15) and (17), 
the equations (15) of mean -mean-motion become identical in form with the equations 
(1) of mean-motion, and the equation (17) of energy of mean-mean-motion becomes 
identical in form -with the equation (3) of energy of mean-motion. 

These equations, obtained from (15) and (17) being equally true with equations (1) 
and (3), the mean-mean-motion in the former being taken over the space S x instead of 
S as in the latter, then, instead of equation (9), we should have for the value of the 
last term—* 

U 2 



148 PROFESSOR 0. REYNOLDS ON INCOMPRESSIBLE VISCOUS 

du , . d («H) , , , du . . „ 

p xx - + dc., = -^ + l?rf-±&c (25) 

in which the right member expresses the rate at which heat is converted into energy 
of mean-mean-motion, together with the rate at which energy of relative-mean-motion 
is transformed into energy of mean- mean-motion ; while equation (19) shows whence 
the transformed energy is derived. 

The similarity of the parts taken by the transformation of mean-mean-motion into 
relative-mean-motion, and the conversion of mean-motion into heat, indicates that 
these parts are identical in form ; or that the conversion of mean-motion into heat is 
the result of transformation, and is expressible by a transformation function similar 
in form to that for relative-mean-motion, but in which the components of relative 
motion are the components of the heat-motions and the density is the actual density 
at each point. Whence it would appear that the general equations, of which equations 
(19) and (16) are respectively the adaptations to the special condition of uniform 
density, must, by indicating the properties of matter involved, afford mechanical 
explanations of the law of universal dissipation of energy and of the second law of 
thermodynamics. 

The proof of the existence of a criterion as obtained from the equations is quite 
independent of the properties and mechanical principles on which the effect of the 
variations of mean-mean-motion on the distribution of relative mean-motion depends. 
And as the study of these properties and principles requires the inclusion of condi- 
tions which are not included in the equations of mean-motion of incompressible fluid, 
it does not come within the purpose of this paper. It is therefore reserved for 
separate investigation by a more general method. 



The Criterion of Steady Mean-motion. 

23. As already pointed out, it appears from the discriminating equation that the 
possibility of the maintenance of a state of relative-mean-motion depends on p/p, the 
variation of mean-mean-motion and the periods of the relative-mean-motion. 

Thus, if the mean-mean-motion is in direction x only, and varies in direction y 
only, if u, v', w are periodic in directions x, y, z, a being the largest period in space, 
so that their integrals over a distance a in direction x are zero, and if the co-efficients 
of all the periodic factors are a, then putting 

± du/dy = C-\ ; 

taking the integrals, over the space a 3 of the 18 squares and products in the last 
term on the left of the discriminating equation (24) to be 



FLUIDS AND THE DETERMINATION OF THE CRITERION. 149 

- 18^C 3 (2Tr/a) a a?a? 
the integral of the first term over the same space cannot be greater than 

Then, by the discriminating equation, if the mean-energy of relative-mean-motion is 
to be maintained, 

pCj 2 is greater than 700 ju./« 3 , 
or 

?V(S)*=™>- • •' w 

is a condition under which relative-mean-motion cannot be maintained in a fluid of 
which the mean-mean-motion is constant in the direction of mean-mean-motion, and 
subject to a uniform variation at right angles to the direction of mean-mean-motion. 
It is not the actual limit, to obtain which it would be necessary to determine the actual 
forms of the periodic function for u, v , w ', which would satisfy the equations of 
motion (15), (16), as well as the equation of continuity (13), and to do this the 
functions would be of the form 

A ; . cos < r ( nt + — x 

where r has the values 1, 2, 3, &c. It may be shown, however, that the retention of 
the terms in the periodic series in which r is greater than unity would increase the 
numerical value of the limit. 

24. It thus appears that the existence of the condition (26) within which no 
relative-mean-motion, completely periodic in the distance a, can be maintained, is a 
proof of the existence, for the same variation of mean-mean-motion, of an actual 
limit of which the numerical value is between 700 and infinity. 

In viscous fluids, experience shows that the further kinematical conditions imposed 
by the equations of motion do not prevent such relative-mean-motion. Hence for 
such fluids equation (26) proves the actual limit, which discriminates between the 
possibility and impossibility of relative-mean-motion completely periodic in a space a, 
is greater than 700. 

Putting equation (26) in the form 

y/idu/dyf = 700 /x/pa 3 , 

it at once appears that this condition does not furnish a criterion as to the possibility 
of the maintenance of relative-mean-motion, irrespective of its periods, for a certain 
condition of variation of mean-mean-motion. For by taking a 2 large enough, such 
relative-mean-motion would be rendered possible whatever might be the variation of 
the mean-mean-motion. 



150 PROFESSOR 0. REYNOLDS ON INCOMPRESSIBLE VISCOUS 

The existence of a criterion is thus seen to depend on the existence of certain 
restrictions to the value of the periods of relative- mean-motion — on the existence of 
conditions which impose superior limits on the values of a. 

Such limits to the maximum values of a may arise from various causes. If du/dy 
is periodic, the period would impose such a limit, hut the only restrictions which it is 
my purpose to consider in this paper, are those which arise from the solid surfaces 
between which the fluid flows. These restrictions are of two kinds — restrictions to 
the motions normal to the sui-faces, and restrictions tangential to the surfaces—the 
former are easily defined, the latter depend for their definition on the evidence to he 
obtained from experiments such as those of Poiseuille, and I shall proceed to show 
that these restrictions impose a limit to the value of a, which is proportional to D, 
the dimension between the surfaces. In which case, if 

s /\duldyf=JJIT>, 

equation (26) affords a proof of the existence of a criterion 

pDU/^K . (27) 

of the conditions of mean -mean-motion under which relative or sinuous-motion can 
continuously exist in the case of a viscous fluid between two continuous surfaces 
perpendicular to the direction y, one of which is maintained at rest, and the other in 
uniform tangential-motion in the direction x with velocity U. 

Section TIL 

The Criterion of the Conditions under which Relative-mean-motion cannot be main- 
tained in the case of Incompressible Fluid in Uniform Symmetrical Mean-flow 
between Parallel Solid Surfaces. — Expression for the Resistance. 

25. The only conditions under which definite experimental evidence as to the value 
of the criterion has as yet been obtained are those of steady flow through a straight 
round tube of uniform bore ; and for this reason it would seem desirable to choose 
for theoretical application the case of a round tube. But inasmuch as the application 
of the theory is only carried to the point of affording a proof of the existence of an 
inferior limit to the value of the criterion which shall be greater than a certain 
quantity determined by the density and viscosity of the fluid and the conditions of 
flow, and as the necessary expressions for the round tube are much more complex 
than those for parallel plane surfaces, the conditions here considered are those defined 
by such surfaces. 



FLUIDS AND THE DETERMINATION OF THE CRITERION. 151 

Case I. Conditions. 

26. The fluid is of constant density p and viscosity /jl, and is caused to flow, by 

a uniform variation of pressure dp/dx, in direction x between parallel surfaces, 
given by 

y = - K y = h (28), 

the surfaces being of indefinite extent in directions z and x. 

Tlie Boundary Conditions. 
(1.) There can be no motion normal to the solid surfaces, therefore 

v = when y = ± b (29). 

(2.) That there shall be no tangential motion at the surface, therefore 

u = w = when y = ± b (30) ; 

whence by equation (21), putting u for u', p yx = — fxdtc/dy. 

By the equation of continuity du/dx + dv/dy + dwjdz = 0, therefore at the 
boundaries we have the further conditions, that when y = ± & , 

du/dx = dv/dy = dwjdz = (31). 



Singular Solution. 

27. If the mean-motion is everywhere in direction x, then, by the equation of 
continuity, it is constant in this direction, and as shown (Art. 8) the periods of mean- 
motion are infinite, and the equations (1), (3), and (9) are strictly true. Hence if 

v = w = u = v = w = (32), 

we have conditions under which a singular solution of the equations, applied to this 
case, is possible whatsoever may be the value of 6 n , dp/dx, p and jx. 

Substituting for_p^, p ys , &c, in equations (l) from equations (21), and substituting 
u for u', &c, these become 

du dp , fdho d~u\ . . 

^=-i+K<¥ + ^) (33) - 



152 



PROFESSOR 0. REYNOLDS ON INCOMPRESSIBLE VISCOUS 



This equation does not admit of solution from a state of rest ;* but assuming a 
condition of steady motion such that dujdt is everywhere zero, and dpjdx constant, 
the solution of 



if 



is 



fi /dht, d,-u\ 1 dp 

~p ' ^/ : + ~dz?) ~ ~J Ika ~~ ' 

u = du/dz = when y = i b , \- 

1 dpf-bj 



u = 



P 



dx 



(34). 



This is a possible condition of steady motion in which the periods of u according to 
Art. 8 are infinite ; so that the equations for mean-motion as affected by heat- 
motion, by Art. 8, are exact, whatever may be the values of 

u, b , p, /j-, and dpjdx. 

The last of equations (34) is thus seen to be a singular solution of the equations (15) 
for steady mean-flow, or steady mean-mean-motion, when it.', v, iv ', p', &c, have 
severally the values zero, and so the equations (16) of relative-mean -motion are 
identically satisfied. 

In order to distinguish the singular values of w, I put 



u 



whence 



= U, \u dy = 2b ~U m ; 



# _ __ -V TT TT _ 
7 to ^ m j ^ 

do: o n - 



TJ, 



V-y 3 



(35). 



J 



According to the equations such a singular solution is always possible where the 
conditions can be realized, but the manner in which this solution of the equation (1) 
of mean-motion is obtained affords no indication as to whether or not it is the only 
solution — as to whether or not the conditions can be realised. This can only be 
ascertained either by comparing the results as given by such solutions with the results 
obtained by experiment, or by observing the manner of motion of the fluid, as in my 
experiments with colour bands. 

* In a paper on the " Equations of Motion and the Boundary Conditions of Viscous Fluid," read 
before Section A at the meeting of the B.A., 1883, I pointed out the significance of this disability to be 
integrated, as indicating the necessity of the retention of terms of higher orders to complete the 
equations, and advanced certain confirmatory evidence as deduced from the theory of gases. The paper 
was not published, as I hoped to be able to obtain evidence of a more definite cbaracter, such as that 
which is now adduced in Articles 7 and 8 of this paper, which shows that the equations are incomplete, 
except for steady motion, and that to render them integrable from rest the terms of higher orders must 
be retained, and thus confirms the argument I advanced, and completely explains the anomaly. 



FLUIDS AND THE DETERMINATION OF THE CRITERION. 153 

The fact that these conditions are realized, under certain circumstances, has afforded 
the only means of verifying the truth of the assumptions as to the boundary con- 
ditions, that there shall be no slipping, and as to /x being independent of the 
variations of mean-motion. 



Verification of the Assumptions in the Equation of Viscous Fluid. 

28. As applied to the conditions of Poiseuille's experiments and similar experi- 
ments made since, the results obtained from the theory are found to agree throughout 
the entire range so long as u', v, w are zero, showing that if there were any slipping 
it must have been less than the thousandth part of the mean flow, although the 
tangential force at the boundary was 0'2 gr. per square centimetre, or over 6 lbs. per 
square foot, the mean flow 376 millims. (l"23 feet) per second, and 

du/dr = 215,000, 

the diameter of this tube being 0"014 millim., the length 1 25 millims., and the 
head 30 inches of mercury. 

Considering that the skin resistance of a steamer going at 25 knots is not 6 lbs. 
per square foot, it appears that the assumptions as to the boundary conditions and 
the constancy of ju, have been verified under more exigent circumstances, both as 
regards tangential resistance and rate of variation of tangential stress, than occur in 
anything but exceptional cases. 



Evidence that other Solutions are possible. 

29. The fact that steady mean-motion is almost confined to capillary tubes — and 
that in larger tubes, except when the motion is almost insensibly slow, the mean- 
motion is sinuous and full of eddies, is abundant evidence of the possibility, under 
certain conditions, of solutions other than the singular solutions. 

In such solutions u', v', to have values, which are maintained, not as a system of 
steady periodic motion, but such as has a steady effect on the mean flow through the 
tube ; and equations (l) are only approximately true. 



The Application of the Equations of the Mean- and Relative-mean-motion. 

30. Since the components of mean-mean -motion in directions y and z are zero, and 
the mean flow is steady, 

v = 0, w=0, du/dt = 0, du/dx=Q ..... (36),. 

HDCCCXCV. — A. X 



154 PROFESSOR 0. REYNOLDS ON INCOMPRESSIBLE VISCOUS 

and as the mean values of functions of u', v , w are constant in the direction of flow, 

d(v!v!) 



= . *&! = « 



d («/«') 



= 0, &C. 



dx dx dx 

By equations (21) and (37) the equations (15) of mean-motion become 



die dp Idru d?u\ \ d ,—j—r, d ,—,—, 



(37). 



p 


dv 
~dt 


= 


dp 


p 


dw 
dt 


— 


dp 

~ dz 



dy 

d 



-P [*<?*) + *<?*)] \ 



(38). 



+ p\ d dy (w-v') + ±{ww)^ y 



The equation of energy of mean-mean-motion (17) becomes 



dt 



iz) + £ (» *£)}- P {aj( u uv ) + ^( U ' ¥W ) } 



— dp 
dx 



dy \ dy) ' d, 

\dyf ' ^/l+^P^^^I j 

Similarly the equation of mean-energy of relative-mean-motion (19) becomes 



\ (duV- , fduV] \-T-rdu - l —,du] 

Ml(^.)+(jr +p\ uv ^ + uw d -\ 



)■ (39). 



-JT = ~ fy\. u \Py* + u ' v ') + v ' {p'n + «^) + v/ {p'y, + w'v)] 



dt 



— 3r[ w ' (P'« + w "0 + L '' (.P'-y + v '™) + ">' ( P'~ + M>V)] 



• {(f J + (£/ +©'}+(?+ :;it + (f + £) s + (£ + £)'. 

-p|»« £-+!*«£-]• (40). 

Integrating in directions ?/ and 2 between the boundaries and taking note of the 

boundary conditions by which u, u, v', w' vanish at the boundaries together with the 
integrals, in direction z, of 



d 



d 



the integral equation of energy of mean-mean-motion becomes 

■dp , f fdu \ 3 , /du \ 2 1 f -r-7 <*"■ i 7773 du n 



fjf**=-lf 






.fr*"** 



cfo/ efe . (41). 



FLUIDS AND THE DETERMINATION OF THE CRITERION. 
The integral equation of energy of relative-mean-motion becomes 



155 



fjf**~jf 



**-<#(£/*(?) 



+ 



7—r du , — ; — - du 1 " 
P\ UV 7y +UW &}. 

rfy ' dz ) + yfc + dx I + V& + dy ) _ 



AftA" , ma 8 , A^ 



+ 



dz 



dy dz 



(42). 



If the mean-mean-motion is steady it appears from equation (41) that 



ff 



dx 



~r^dy dz, 



the work done on the mean-mean-motion u, per unit of length of the tube, by the 
constant variation of pressure, is in part transformed into energy of relative-mean- 
motion at a rate expressed by the transformation function 



ff 



,-,— du - 7 — r dw\ 
p[uv -^+uw-)dydz 



and in part transformed into heat at the rate 



"ff 



duY 2 /du\~ 
l\dy) + \d~z 



dy dz. 



While the equation (42) for the integral energy of relative-mean-motion shows 
that the only energy received by the relative-mean-motion is that transformed from 
mean-mean-motion, and the only energy lost by relative-mean-motion is that 
converted into heat by the relative-mean -motion at the rate expressed by the last 



term. 



And hence if the integral of E' is maintained constant, the rate of transformation 
from energy of mean-mean-motion must be equal to the rate at which energy of 
relative-mean-motion is converted into heat, and the discriminating equation becomes 

f H^ I + « f ) ** = -<* ffH(D ! + (SJ + (f )'} 



The Conditions to be Satisfied by u and u, v, w'. 



31. If the mean-mean-motion is steady u must satisfy : — 

x2 



156 PROFESSOR 0. REYNOLDS ON INCOMPRESSIBLE VISCOUS 

(1) The boundary conditions 

u = when y == ± b (44) ; 

(2) The equation of continuity 

du/dx = . (45); 

(3) The first of the equations of motion (38) 

dp fcPu , d*u\ f d r-r-y. , d .—, — -,. 1 

or putting 

u = U + u — IT and djj/dx = jj, d~U/dy 2 

as in the singular solution, equation (48) becomes 

fc P(u-U) d*(u-V)\ \d / -^- d -r-y] 

(4) The integral of (47) over the section of which the left member is zero, and 

the mean value of li dujdy = /x dJJ/dy when y = i ^o • • • (48). 

From the condition (3) it follows that if u is to be symmetrical with respect to the 
boundary surfaces, the relative-mean-motion must extend throughout the tube, so 
that 



I— - -f —j~ ) dz is a function of y z . . . . . . (49). 

And as this condition is necessary, in order that the equations (38) of mean-mean- 
motion and the equations (16) of relative-mean-motion may be satisfied for steady 
mean-motion, it is assumed as one of the conditions for which the criterion is sought. 
The components of relative-mean-motion must satisfy the periodic conditions as 
expressed in equations (12), which become, putting 2c for the limit in direction z, 

(1) r« r« t /■»• 

u dx = \v dx = iv dx = i 

Jo Jo Jo , 

>- (50). 

u dy dz = 

J - i J - c J 

(2) The equation of continuity 

du'/dx + dv'jdy -\- dw'/dz = 0. 



FLUIDS A.ND THE DETERMINATION" OF THE CRITERION". 157 

(3) The boundary conditions which with the continuity give 

u' = v = w' = du'jdx = dv'jdy = div'jdz = when y = ± b . . (51). 

(4) The condition imposed by symmetrical mean-motion 

f_.(f + ! f : )* = w> m 

These conditions (l to 4) must be satisfied if the effect on u is to be symmetrical 
however arbitrarily u, v , w' may be superimposed on the mean-motion which results 
from a singular solution. 

(5) If the mean-motion is to remain steady u', v , iv must also satisfy the kine- 

matical conditions obtained by eliminating p from the equations of mean-mean-motion 
(38) and those obtained by eliminating p' from the equations of relative-mean- 
motion (16). 

Conditions (1 to 4) determine an inferior Limit to the Criterion. 

32. The determination of the kinematic conditions (5) is, however, practically 
impossible ; but if they are satisfied, u', v, w must satisfy the more general conditions 
imposed by the discriminating equation. From which it appears that when u, v, to 

are such as satisfy the conditions (l to 4), however small their values relative to u 
may be, if they be such that the rate of conversion of energy of relative-mean-motion 
into heat is greater than the rate of transformation of energy of mean-mean-motion 
into relative -mean-motion, the energy of relative-mean-motion must be diminishing. 
Whence, when u, v', w' are taken such periodic functions of x, y, z, as under 
conditions (1 to 4) render the value of the transformation function relative to the 
value of the conversion function a maximum, if this ratio is less than unity, the 
maintenance of any relative-mean-motion is impossible. And whatever further 
restrictions might be imposed by the kinematical conditions, the existence of an 
inferior limit to the criterion is proved. 

Expressions for the Components of possible Relative-mean-motion. 

33. To satisfy the first three of the equations (50) the expressions for u, v, w', must 
be continuous periodic functions of x, with a maximum periodic distance a, such as 
satisfy the conditions of continuity. 

Putting 

/ = Itrja ; and n for any number from 1 to oo , 



158 PROFESSOR 0. REYNOLDS ON INCOMPRESSIBLE VISCOUS 

and 

u ' = - {($ + S 1 ) cos (« fa ) + (^ + f ) sin w} ] 

?/ = %q {nla„ sin (nZcc) — nl{3„ cos («Zas)} ,' \ ' /» 

w = £" {«Zy„ sin (nix) — nZ S„ cos (nix)} J 

«', v', ?(/ satisfy the equation of continuity. And, if 



a = /3 = y = S= da/dy = d/3/dy = dy/dz = dS/dz = when y = ± bo 
and a/3, ay, aS are all functions of if only 



(54), 



it would seem that the expressions are the most general possible for the components 
of relative-mean-motion. 

Cylindrical-relative-motion. 

34. If the relative-mean-motion, like the mean-mean-motion, is restricted to 
motion parallel to the plane of xy, 

y = <5 = w' = 0, everywhere, 

and the equations (53) express the most general forms for u, v in case of such 
cylindrical disturbance. 

Such a restriction is perfectly arbitrary, and having regard to the kinematical 
restrictions, over and above those contained in the discriminating equation, would 
entirely change the character of the problem. But as no account of these extra 
kinematical restrictions is taken in determining the limit to the criterion, and as it 
appears from trial that the value found for this limit is essentially the same, whether 
the relative-mean-motion is general or cylindrical, I only give here the considerably 
simpler analyses for the cylindrical motion. 

The Functions of Transformation of Energy and Conversion to Heat for Cylindrical 

Motion. 
35. Putting 

for the rate at -which energy of relative-mean -motion is converted to heat per unit of 
volume, expressed in the right-hand member of the discriminating equation (43), 



Fluids and the determination of the criterion. 



159 



Then substituting for the values of u, v, w' from equations (53). and integrating in 
direction as over 2-rr/l, and omitting terms the integral of which, in direction y, vanishes 
by the boundary conditions, 

In a similar manner, substituting for u v, integrating, and omitting terras which 
vanish on integration, the rate of transformation of energy from mean-mean-motion, 
as expressed by the left member in the discriminating equation (43), becomes 



\\puv' d f y dy dz = i f j* Li (a n ^ - a, cl fy i 



dy 



dy dz 



(58). 



And, since by Arb. 31, conditions (3) equation (47), 



* I <»- u > =/>!<**>■ ■ w 



integrating and remembering the boundary conditions, 

fj. — (w — U) = pwV, /a (w — U) = p u'v dy 

And since at the boundary u — U is zero, 



(60). 



(u'v')dy = (61). 



Whence, putting U+ u — U for u in the right member of equation (58), substituting 
for u — U from (60), integrating by parts, and remembering that 



also that 



-r-T = -3^', which is constant. , (62), 

dy V 



uV = **{**(«. ^-&^)} (63), 

we have for the transformation function 



= i 



160 PEOFESSOR O. REYNOLDS ON INCOMPRESSIBLE VISCOUS 

If u, v are indefinitely small the last term, which is of the fourth degree, may be 
neglected. 

Substituting in the discriminating equation (43) this may be put in the form 



2phoUm _ 2 V \\frp («„* + A, 2 ) + 2nW 



dyj + \dy 



P 



°\UiW^--t)h 



+<M±(i)> (65 , 



Limits to the Periods. 

36. As functions of y the variations of a„, fi n are subject to the restrictions imposed 
by the boundary conditions, and in consequence their periodic distances are subject 
to superior limits determined by 2& , the distance between the fixed surfaces. 

In direction x, however, there is no such direct connection between the value of b^ 
and the limits to the periodic distance, as expressed by 2ir/nl. Such limits necessai'ily 
exist, and are related to the limits of a u and /3„ in consequence of the kinemetical 
conditions necessary to satisfy the equations of motion for steady mean-mean- 
motion ; these relations, however, cannot be exactly determined without obtaining a 
general solution of the equations. 

But from the form of the discriminating equation (43) it appears that no such exact 
determination is necessary in order to prove the inferior limit to the criterion. 

The boundaries impose the same limits on a,„ /3„ whatever may be the value of nl ; 
so that if the values of a„, f3„ be determined so that the value of 

2pb a U m . . . 

is a minimum 

for every value of nl, the value of rl, which renders this minimum a minimum- 
minimum may then be determined, and so a limit found to which the value of the 
complete expression approaches, as the series in both numerator and denominator 
become more convergent for values of nl differing in both directions from rl. 

Putting /, a, /3 for rl, a,, /3 r respectively, and jjutting for the limiting value to be 
found for the criterion 

K 1 = ^^ (66) 



f° {z>s + /3 2 ) + 2Z 2 



\dy) ~ + " \dy. 



-K = b • 

2 1 ° r* p 1 da dj3\ 



+®r+(^i-- 



(67) 



when a and /3 are such functions of y that K 2 is a minimum whatever the value of I, 
and I is so determined as to render K x a minimum-minimum. 



FLUIDS AND THE DETERMINATION OF THE CRITERION. 161 

Having regard to the boundary conditions, Sec, and omitting all possible terms 
which increase the numerator without affecting the denominator, the most general 
form appears to be 

a = 1 " [a 2s+1 sin (2s -j- l)p], ~) 

/3 = S " \b it sin (2tp)l y " . . (68). 

where 

P = ^/2& . - J 

To satisfy the boundary conditions 

.? = 2r, when s is even, s = 2r + 1, when s is odd. 

t = 2r + 1, when t is odd, t = 2 (r -J- l), when t is even. 

Since a = 0, when p = ± ^77, 

> • (69). 
and since dfijdy = 0, when p = ± 2 7T > 

S "{- (4r + 2) 6 4 , +2 + 4 (r+ 1) 6 4r+4 } = oj 

From the form of K x it is clear that every term in the series for a and f3 increases 
the value of K : and to an extent depending on the value of r. K. 1 will therefore be 
minimum, when 

a = a. sin p 4- a, sin 3p 

. . } (70), 

ft = b 2 sin 2p + \ sin ip 

which satisfy the boundary conditions if 

= a, I 

(n). 



C'o — C'l 



b 2 = 2b± 



Therefore we have, as the values of a and /3, which render K x a minimum for 
any value of I 

a/«j = sin p -\- sin Sp, j3/b z = sin 2p + J sin 4p. 
And 

- — = cos p + 3 cos 3», — - -r = 2 cos 2p + 2 cos Ap r ■ ('^) 

^ 7^ ~ ^7H Z '- 3 smp - 3 sm 3p + sin 5p + sm 7jp} J 



Traji, \ cly dy 

MDCCOXCV. — A. 



162 PROFESSOR O. REYNOLDS ON INCOMPRESSIBLE VISCOUS 

and integrating twice 



Putting 



— L for I, 



2&o 



3 

the denominator of -K 1; equation (67), becomes 



- 1-325 Lg^&j. 
In a similar manner the numerator is found to be 



7T N* 



& * {—) {L 4 (2a 1 2 + 1-256/) + 2L 2 (lOc^ 2 + 8fc 2 2 ) + 82^ + 80&„ 2 }, 

and as the coefficients of a x and b. 2 are nearly equal in the numerator, no sensible error 
will be introduced by putting 

h = - a lt 
then 

3^ L* + 2 x 5-53L* + 50 /ir\* ,„ A . 



2 ' 0-408L \2, 

which is a minimum if 

L= 1-62 (75) 

and 

K X = 5I7 (76). 

Hence, for a flat tube of unlimited breadth, the criterion 

p 2b U, ll /ix is greater than 517 . *. (77). 

37. This value must be less than that of the criterion for similar circumstances. 
How much less it is impossible to determine theoretically without effecting a general 
solution of the equations ; and, as far as T am aware, no experiments have been made 
in a flat tube. Nor can the experimental value 1900, which I obtained for the round 
tube, be taken as indicative of the value for a flat tube, except that, both theoretically 
and practically, the critical value of U,„ is found to vary inversely as the hydraulic 
mean depth, which would indicate that, as the hydraulic mean depth in a flat tube is 
double that for a round tube, the criterion would be half the value, in which case the 
limit found for K x would be about 0'61 K. This is sufficient to show that the 
absolute theoretical limit found is of the same order of magnitude as the experimental 



FLUIDS AND THE DETERMINATION OF THE CRITERION. 



163 



value : so that the latter verifies the theory, which, in its turn, affords an explanation 
of the observed facts. 



The State of Steady Mean-motion above the Critical Value. 



38. In order to arrive at the limit for the criterion it has been necessary to consider 
the smallest values of u , v, w , and the terms in the discriminating equation of the 
fourth degree have been neglected. This, however, is only necessary for the limit, 
and, preserving these higher terms, the discriminating equation affords an expression 
for the resistance in the case of steady mean-mean-motion. 

The complete value of the function of transformation as given in equation (64) is 



-r-rdll\ 

pUV ly) 



- s 



3U„, f\ n I dfo d*A , p 2 f*». , / d/3„ 

f w J-t \-i r ^ ~ A * ) d)J + ^ Uf } (*• -dj 



'*?* 



(77 a). 



Whence putting IT + u — U, for u in the left member of equation (77), and inte- 
grating by parts, remembering the conditions, this member becomes 

^dy¥pu^dy+£?\u'v'Ydy ...... (78), 



in which the first term corresponds with the first term in the right member of 
equation (64), which was all that was retained for the criterion, and the second term 
corresponds with the second term in equation (64), which was neglected. 
Since by equation (35) 

3 J^=_J^ (78tt)) 



V 



f* 



dx 



we have, substituting in the discriminating equation (43), either 



2 1 Jl &p_ 

3 P ^ dx 



or 



Therefore, as long as 



2b, 

o 
O 



M'^fw+tfrr* 



dy uv dy 

-in J -4n 



dhb dp 



dx 



2 V d P 
V 
Y 2 



5 P *» dx 



(79), 



(80). 



164 PROFESSOR O. REYNOLDS ON INCOMPRESSIBLE VISCODS FLUIDS. 

is of constant value, there is dynamical similarity under geometrically similar circum- 
stances. 

The equation (79) shows that, 






when — § p ~y — is greater than K, 



u'v must be finite, and such that the last term in the numerator limits the rate of 



transformation, and thus prevents further increase of u'v. 

The last term in the numerator of equation (79) is of the order and degree 

p a L*a*//j, 8 as compared with L*a 2 



the order and degree of — — ( P ~H.') the first term in the numerator. 



1_ d 

It is thus easy to see how the limit comes in. It is also seen from equation (79) 
that, above the critical value, the law of resistance is very complex and difficult of 
interpretation, except in so far as showing that the resistance varies as a power of the 
velocity higher than the first. 



[ 165 j 



V. On a Method of Determining the Thermal Conductivity of Metals, ivith 
Applications to Copper, Silver, Gold, and Platinum. 

By James H. Gray, M.A., B.Sc, late " 1851 Exhibition " Scholar, Glasgow University, 

Communicated by Lord Kelvin, P.R.S. 

Received May 24, — Read June 14, 1894 ; Re-cast, with Additions, January 31, 1895. 

Of the different methods hitherto employed for the determination of thermal conduc- 
tivity of metals, only those which were elaborated by Foebes and by Angstrom have 
been successful in giving absolute results with fair approach to accuracy. The two 
methods, in the hands of these and subsequent experimenters, have given closely 
concordant results, both for copper and for iron. They, however, possess the dis- 
advantages of being exceedingly elaborate, requiring, as they do, very extensive 
preparations and comparatively large masses of the metals which are to be tested. 
For this reason, only the less costly metals can be tested, as it would be impracticably 
expensive to obtain a bar of gold or platinum, for example, a metre or more in length, 
and perhaps 2 square centims. section. 

The method used in the present investigation (for which a grant of £50 was obtained 
from the Government Research Fund) is free from these objections. It was suggested 
by Lord Kelvin as far back as thirty years ago, about the same time that the late 
Principal Forbes began his experimental inquiry as to whether thermal conductivity 
varied with temperature. The chief advantages of this method are that (1) it is 
much simpler than the others ; (2) a test of the conductivity of any metal can be 
made in two or three hours ; and (3) (perhaps most important of all) only a few 
grammes of the metal are necessary. Thus, even the rarest and most expensive 
metals can be tested, at very moderate cost. 

The method is essentially the experimental realization of the theoretical conditions 
implied in the fundamental formula 

Q = kA'^~- u t 

where the symbols have their usual meaning. The metals to be tested are made in 
the form of wires of circular section. One end is kept at a constant temperature v, 
and the flow of heat Q, in a given time t, is measured. The length and section 
being known, all the data are obtained for the determination of the absolute value of 

30.5.95 



166 



MR. J. H. GRAY ON A METHOD OF DETERMINING 



the thermal conductivity. It will be noted that this value is the proper mean 
conductivity corresponding to the range of temperature between the ends of the wire. 
Fig. 1 is a perspective drawing of the apparatus which has been used in the tests 
of this method. Fig. 2 is a section (all the parts being drawn quarter full size) 
containing the axis of the wire to be tested. Fig. 3 is a section, drawn full size, 
through the middle of the apparatus, in a plane perpendicular to the section in fig. 2, 
and showing in greater detail the wire, calorimeter ball, and that part of the heating 
box at which the wire is soldered. 



Fie. 1. 





Quarter full size. 



Referring to fig. 2, W is the wire to be tested. The upper end of W is soldered 
into the bottom of the copper box B, and the lower end into the solid copper ball C, 
the diameter of which is 5 "5 centims. The sides of the copper box B are of thin 
sheet copper, and the bottom of copper, 3 millims. thick. B is supported at the 
middle by being fitted into a rectangular hole in a wooden screen, L, of dimensions 
60 X 60 centims., by 2 centims. thick. In the hole of the copper block K, a small 
thermometer is inserted for measuring the temperature of the other end of the wire. 
The box B is filled with water and kept boiling briskly. The ball C is the calori- 
meter by which the amount of heat conducted by the wire W is measured. In order 
to measure the temperature of C, a very sensitive thermometer, which can be read to 
one-fortieth of a degree Centigrade, is inserted in a hole drilled in G. This hole 
reaches to a depth of 3 '6 centims. from the circumference of the ball. The bulb 
of the thermometer in the ball is surrounded by water or mercury. Surrounding 



THE THERMAL CONDUCTIVITY OF METALS. 



167 



the heating box, B, is an asbestos covering, M, to prevent heat from reaching the 
calorimeter from the sides of the box. In order to keep the temperature of the air 
surrounding the calorimeter constant, the latter is surrounded by a water-jacket, B, 
through which water at the temperature of the air is kept circulating. This water- 
jacket is simply a cylindrical vessel, made of copper, with double walls, between 
which the water circulates. The inside diameter is about 1 centim. greater than that 
of the ball. The top of the water-jacket is covered with three or four layers of 

Fig. 3. 



i 




Full size. 



paper, so that the air surrounding the ball is completely separated from the outside 
air, and is kept at a constant temperature. Surrounding the wire, all along its 
length, is a tube of cardboard, G, of inside diameter 1 centim. Between the wire 
and the inside of the tube cotton-wool is loosely packed, so as to prevent, as 
effectually as possible, circulation of air about the wire. 

From fig. 2 it will be seen that the heat from the Bunsen is prevented from 



168 MR. J. H. GRAY ON A METHOD OF DETERMINING 

reaching the wire or the ball by the wooden screen L. In the bottom of the box, 
just above the Bunsen, are riveted a number of copper pins, so as to catch and 
distribute the heat of the burner. Fig. 4 shows a plan of the box. 

Fig-. 4. 



© 



o o o o o 
ooo o o 

O O O 00 

o o o o o 

o o o o o 



Quarter full size. 

It will be convenient to classify the sources of error that may affect the results, 
and to deal with them at this point. 

1. There is, unless proper precautions be taken, loss of heat due to radiation from 
the surface of the wire, and therefore the value obtained for the conductivity will be 
too low. 

2. The temperature indicated by the thermometer in the hot water may not be the 
same as that of the end of the wire at the point where it enters the box. Also, the 
temperature of the ball may not be the same throughout. 

3. The thermometer may not indicate the average temperature throughout the ball. 

4. There may be a lag in the thermometer. 

5. There may be some error due to the solder at the ends of the wire. 

1 . Loss of heat due to radiation from the surface of the wire. As this was the most 
obvious source of error, a long time was spent and much work done in investigating it. 

The cardboard tube G (fig. 2) was found to be thoroughly efficient in preventing 
radiation. It can be very easily made by rolling a long strip of paper, which has 
been previously gummed on one side, several times round a circular rod of a centimetre 
diameter. The length of the tube is a little less than that of the wire. After the 
gum has dried, a slit sufficiently wide to admit the wire is cut parallel to the length. 
A circular piece of cardboard is fixed with gum to one end of the tube, as a flange for 
attaching the tube to the bottom of the heating box. After it has been arranged 
that the wire is in the central line, cotton-wool is put loosely in and the slit closed 
up with gummed paper. The small volume of air in this tube takes almost imme- 
diately the temperature of the wire all along its length. 

To test the efficiency of the tube, a large number of experiments was made, the 
results of which are given further on (pp. 180, 181). It is clear that for a given differ- 
ence of temperature between the ends, the loss by radiation from the surface of a wire 
of given diameter will be greater the greater the length. If, then, there be no error 
which becomes less the greater the length, and thus compensates for the radiation error, 
a sufficient test of the efficiency of the tube will be to determine the conductivity with 
different lengths of the same wire. The shorter lengths ought to give a distinctly 
higher value, since the radiation from the surface is not only less than in the longer 



THE THERMAL CONDUCTIVITY OF METALS. 169 

lengths, but the quantity of heat conducted along the wire per second is greater, and 
therefore the percentage error due to radiation rapidly diminishes. 

In order to determine a superior limit for the error due to loss of heat by radiation, 
a calculation is made below. The numbers used are taken so as to be as unfavourable 
as possible, and give a value much higher than what would practically turn out. 

In the case of copper wire, the surface was always somewhat tarnished, so the 
emissivity may be taken as intermediate between those of polished and blackened 
copper, that is '0008. The diameter and length of wire were respectively "2 centim. 
and 4 centims. The temperature at the hot end was 98° C, at the cold end 14° C 
The curve of temperature along' the wire being logarithmic, the mean temperature 
will be considerably less than half the sum of the highest and lowest temperatures, 
which would assume that the curve is a straight line passing through the highest and 
lowest points. Take, however, the curve to be a straight line ; then the mean tempe- 
rature above that of the air is 42° C. The quantity of heat Q, lost from the surface 
S, of emissivity E, in one minute, is 

Q = ES X 42 X 60 

= 1'91 C.G.S. units approximately. 

The quantity of heat conducted along the wire during this minute, as taken from 
one of the tests, was "5 x 68'9, '5 being the rise in temperature, and 68'9 the capacity 
of the caloi'imeter. The maximum percentage error clue to radiation in a length of 
4 centims. is therefore 5'5 per cent. This is on the assumption that there is no 
jacket round the wire, but even then the actual loss would probably be less than 
3 per cent, if currents of air be avoided. This rough calculation shows that radiation 
from the surface of the wire need not be considered as an objection to the method. 

2. Possible error due to the fact that the thermometers are not actually at the 
ends of the wire, and so may not be indicating the proper temperatures. 

The effect of this error would also be to give too low a value for the conductivity. 
To guard against this the bottom of the box is made very thick, and the large block 
K (fig. 2) is added so as to hold the thermometer. The difference of temperature 
between the inside and outside surfaces of the bottom of the box is certainly 
exceedingly small, if as much heat as the wire can take away is supplied to it. 
Since the heat is supplied by boiling water, it is, however, possible that the copper 
conducts so quickly that there is always a layer of water, it may be thin, immediately 
in contact with the metal at a very much lower temperature than 100° C. This 
point is particularly emphasized by Lord Kelvin in volume 3 of his Collected Papers, 
where he remarks upon the exceedingly low values obtained by Clement and by 
Peclet for the conductivity of copper. These experimenters both attempted to 
measure the conductivity by keeping one side of a slab of the metal in contact with 
water at a constant temperature and measuring the rise in temperature of a known 

MDCCCXCV. — A. Z 



170 



MR. J. H. GRAY ON A METHOD OF DETERMINING 



quantity of water in contact with the other side. The result was that Clement's 
value was 200 times too small, while Peclet, who tried to avoid Clement's error by- 
having the water violently stirred, succeeded in obtaining a value six times too 
small. With the large surface to carry away the heat, Peclet's method is useless 
for any substance having so high a conductivity as even the worst of the metals, 
since the stirring could never be rapid enough without introducing fresh complications. 

The direct tests applied to determine this error in the present investigation showed 
that the temperatures on the inside and outside of the bottom of the box were the 
same. 

The following approximate calculation serves to show the order of magnitude of 
the error due to the assumption that the thermometer in the ball indicates the 
temperature of the end of the wire. 

It is clear that the difference of temperatures between the wire where it enters the 
hall, and the thermometer will be much less than that found as follows : — 

Take the case of a wire carrying heat to an infinite block of metal whose surface is 



Fig-. 5. 




plane, and remark that the isothermals in the block would be hemispherical surface 

(fig. 5) having for their common centre the point where the axis of the wire enters 

the ball, and suppose the flow of heat to be steady. 

Let 

K = conductivity of the wire, 

Jc = „ „ ball, 

radius of the wire, 



a 



b = 



ball. 



THE THERMAL CONDUCTIVITY OF METALS. 171 

Then the quantity of heat that flows through any hemispherical surface distant r 
from the end of the wire is 



and, since the flow is steady 



Hence 



Q=-*f2^; 



l(-*f 2 "* " 



which gives 



Hence 



whence 



r>— -C 
^ dr - ° 1; 



v = C^- 1 + Co. 
For r = a let v = Y, and for r = b let v = 6. 



V - , , 6b -Ya 

v = ab r l -\ ;— 

b — a 1 1 — a 



dv 7 V - 6 

— = ab r 

dr b — a 



-•: 



-i . 



and 



AJ so 



V — 6 

Q = 2-rrk ab. 

b — a 



Q = (Y 1 -Y)^ 



where Y 1 is the temperature at the hot end of the wire, and / the length of the wire. 
Since V is the temperature of the wire just where it enters the ball, and 6 the 
temperature at the centre of the ball, V — is certainly much greater than the 
error, a superior limit to the magnitude of which we wish to ascertain. The heat 
which flows through the wire must be equal to that which flows into the ball ; 
therefore 



whence 



(Vi — V) — — = Ittk-t— - ab, 

' I b — « 






and, therefore, 



v - e = (Vi - e) 





ft. 
2/5 


K 

Tc 


(6- 

b 


a) 




1 


+ 


a 
21 


K(6 


— 


a) 


k 


b 






z 


2 









172 MR. J. H. GRAY ON A METHOD OF DETERMINING 

In this case "V\ = 100° C, = 15° C, and, since the copper of the wire and ball 
were the same, ~K/k = 1 ; b = 27 millims., a = 1 millim. 
Take Z = 8 centims. ; then, 

y _ e = 85 , ^7%,. = -5° c. 

x ^ ItiO ~2T 

Take I = 3 centims., which is less than the shortest length used ; 

then V - 6 = 85 , ^ f? ^ 1 - 3 o c 

1 + iftrff ' 

Therefore l - 3° C. is greater than the extreme possible error made with the copper 
wire, that is 1*3 in 85, or about 1*5 per cent. 

Several attempts were made to obtain a direct test of this by applying a thermo- 
electric junction to the wire just at the point where it entered the ball. Owing, 
however, to the large mass of the ball which had to be heated, it was found most 
difficult to solder the thin wires of the thermo-electric junction at the required place, 
and, after several unsuccessful attempts, it was given up, as the indirect proof supplied 
by using different lengths of wire seemed quite satisfactory. 

3. The thermometer in the ball may not indicate the average temperature. 

This also would be tested by using different lengths of wire, and, as will be seen, 
the results show that there was no substantial variation. 

4. Lag in the thermometer which measures the rise in temperature of the ball. 
Here again different lengths will be a test. Also, in case that the water round the 
bulb of the thermometer caused the lag, mercury was substituted, but no difference in 
the result was obtained. 

5. The solder at the ends did not cause any difference of value for different 
lengths. 

The method of conducting a test is as follows. 

Take a length of not more than 8 centims. of the wire. As it is very easy to 
obtain any diameter, it will be convenient to have a hole bored in the bottom of the 
heating box, just below the thermometer, of diameter rather more than 2 millims., and 
depth 3 or 4 millims. The heating box must be brazed together, otherwise it is apt 
to fall to pieces when the wire is being soldered in. The latter process can be done 
with ordinary solder. 

The mass of copper in the box being considerable, it is rather a troublesome matter 
to solder the wire into it, as the whole box has to be heated. For this reason a 
soldering iron cannot be used. The box is most easily heated by a blow-pipe flame 
and the wire then inserted. The extra solder is then cleared off, so as to give a 
definite point from which to measure the length. After this end is fixed, the other 
end is soldered in a similar manner to the copper ball, and in the latter case fusible 
solder melting at about 100° C will do quite well. 



THE THERMAL CONDUCTIVITY OP METALS. 173 

It was, however, found that the method of soldering just described, and used in 
this investigation, was very ti'oublesome, and required some practice. If new 
apparatus were being made, it would certainly be much more convenient to make an 
alteration in this respect. 

The following plan would make the soldering of the wire a very easy process, 
instead of, as described, a difficult one. Six copper plugs, each of the shape shown 
in sectional elevation and plan in fig. 6, might be made, 8 millims. in length, 



Fi R . 6. 






__ 




and 1 centim. diameter, so as to screw into a corresponding hole in the bottom of the 
heating box ; and six similar plugs might be made for the ball. In each of the plugs 
the central hole might be made of a different diameter, varying from 2 to 4 millims. 
In this way, wires of different diameters could very easily be soldered into the 
suitable plugs, which could then be screwed, first the one end into the ball, then the 
other end into the box. The two side holes shown in fig. 6 are for the purpose of 
facilitating the screwing in of the plugs. By screwing into the ball first, the possi- 
bility of twisting the wire is avoided. It is advisable not to use wire of diameter 
much less than 2 millims., for, in wires of less diameter, the length required to give a 
readable rise of temperature per minute becomes inconveniently small, unless the 
calorimeter ball is made very small. 

The calorimeter ball most frequently used in the present work was turned from 
the solid, and is 5 - 5 centims. in diameter. This was found to be a very convenient 
size for the metals of high conductivity — for example, gold, silver, and copper. 
Any length from 4 to 8 centims. of wires of these metals may be used without 
making it difficult to read the rise in temperature per minute. It is not advisable 
to use lengths shorter than 4 centims.. as there is then a danger of the water- 
jacket being too near the heating-box, but it is better to use a smaller ball, say 
of 4 centims. diameter, for metals of lower conductivity. For metals having con- 
ductivities between 1'0 and 07 C.G.S. units, the large ball was found to be quite 
convenient ; for lower values the smaller ball was used. The object aimed at was 
to arrange the dimensions so as to enable an experiment to be finished in less than 
half an hour from the time that one end was made hot by the boiling water. 

After the wire has been soldered in, the box is placed in the screen L (fig. 2), and 
fixed by any convenient means, so that the wire hangs vertical, and the asbestos 
cover is put over the box. The cardboard tube, having been made of suitable 
length, and slit along its length, is now slipped round the wire, and, after a little 
cotton is loosely packed in, the slit is closed up by means of a strip of gummed paper. 



174 ME, J. H. GRAY ON A METHOD OF DETERMINING 

The wire is now completely enclosed in this tube, and loosely surrounded by cotton 
wool. 

The thermometer is placed in the hole in the ball, and a little water put in to fill 
up the hole. The water-jacket may then be raised so as to surround the ball, and 
the top of the water-jacket must be covered with two or three sheets of paper, holes 
haviuo- been cut in these, so as to admit the wire and thermometer. 

O 3 

It was found best to make these preparations a few hours before the actual test 
was begun, so as to allow the system to take up a permanent temperature. When it 
has been ascertained that this temperature has been reached, a reading is taken from 
the thermometer in the ball. The thermometer used was most carefully made and 
calibrated for the tests by Mr. Otto Muller, of Glasgow. The whole length of the 
stem is 15 centims., and it is marked off to read twentieths of a degree from 9° to 
20° C. Each division is a half millimetre, so it is perfectly easy to read to one- 
fortieth of one degree. 

Before beginning the test, the water-jacket is lowered, and a vessel containing ice 
and water raised so as to cover a part of the ball. By this means the temperature of 
the ball is lowered by 6° or 7° below that of the air. While this is being done, the 
boiling water is poured into the box, so as to nearly fill it, and the Bunsen lamp lit. 
The water soon begins to boil rapidly, and the thermometer (which is 12 centims. 
long and reads from 95° to 105° C.) indicates a constant temperature, usually 97° or 
98° C. When the temperature of the ball has been lowered 6° or 7°, the ice and 
water are taken away, and the ball is carefully dried with a soft cloth. The water- 
jacket is again placed so as to surround the ball and the cover put on as before, the 
circulation of water in the jacket having been started. 

It is now only necessary to take readings of both thermometers every half minute. 
The temperature of the hot water will be practically constant, but it is advisable 
to take the readings in case of alteration. The calorimeter thermometer may be read 
till it reaches 20° C. 

It will be convenient to explain here the reason for cooling the ball 6° or 7° before 
starting. In the preceding remarks no notice was taken of the fact that there will 
be radiation to or from the surface of the ball unless the latter is at the same tempe- 
ture as its surroundings. It would be impossible to allow for this by calculation, as 
the surface is altered before every test by being heated while the wire is being 
soldered into the ball. For the purpose of getting rid of the necessity of allowing 
for this radiation, the bail is cooled down. 

Let Q t = the quantity of heat which flows along the wire in unit time when the 
hot end is at T° and the cool end at 6° above the temperature t of the air and water- 
jacket, and let Q 3 = the quantity when the cool end is 6° below that of the air. 

Then, assuming that the conductivity does not change very much through 26°, and 
that a, the loss by radiation in unit time when the ball is 9° above the air tempera- 



THE THERMAL CONDUCTIVITY OF METALS. 



175 



ture,- is equal to the gain by absorption in unit time when the ball is 8° below the 
air temperature, we have 

Qi=tIT-(«+^ — 

and 



KA 



Therefore 



Q 2 = ^[T -(*-#)] + 



Q t + Q 2 _ KA _ 



It is seen by the last equation that the effect of radiation to or from the surface of 
the ball is completely eliminated since the coefficient of emission is numerically equal 
to the coefficient of absorption for the same difference of temperatures. It therefore 
fortunately does not matter how the surface of the ball becomes changed, so long as 
it remains the same during the half hour of the experiment. As a matter of fact, 
during the soldering process the surface becomes very much tarnished. 

Table I. gives a specimen experiment taken at random from my laboratory book. 



Friday, 23rd March, 1894. — Pure Silver Wire (annealed). Length = 6 - 59 centims. 
Diameter = - 202 centim. Temperature of Air = 14'3° C. 



I. 


II. 


I. 


II. 


Reading taken every 


Temperature of 


Reading taken every 


Temperature of 


half-minute. 


hot end. 


half-minute. 


hot end. 


°C. 


°C. 


°C. 


°C. 


10-3 


98-2 


14-75 


98-3 


10-5 


98-2 


14-9 


98-4 


10-75 


98-2 


151 


98-6 


10-95 


98-3 


15-25 


98-5 


1115 


98-2 


15-45 


98-6 


11-35 


98-2 


15-6 


98-4 


11-55 


98-3 


15/5 


98-4 


11-75 


98-3 


159 


98-6 


11-95 


98-2 


16-05 


98-5 


12-15 


98-3 


16-25 


98-6 


12-35 


98-2 


16-4 


98-6 


12-55 


98-3 


1655 


98-6 


12-75 


98-5 


16-7 


98-6 


12-.<5 


98-3 


16-85 


98-6 


131 


98-4 


17-0 


98-6 


13-3 


98-3 


17-15 


98-6 


135 


98-4 


173 


98-6 


1365 


98-3 


17-45 


98-6 


13-85 


98-4 


17-6 


98-6 


1405 


98-4 


17-7 


98-7 


14-25 


98-4 


17-86 


98-6 


14-4 


98-4 


18-0 


98-6 


14-6 


98-3 







176 MR. J. H. GRAY ON A METHOD OF DETERMINING 

The numbers in column I. are put on a curve, as shown in diagram II. From this 
curve the rise in temperature in half a minute is read off for x° above the temperature 
of the air, and this is added to the rise for x° below the temperature of the air, where 
x is any value from to 5 or 6. In this way as many as 10 or 15 values are 
obtained. If the curve were quite regular, each of these values would be the same, 
since they each represent the rise in temperature per minute for the same difference 
of temperature, but they are found to vary by about 1 or 2 per cent. But, by taking 
the mean of 10 or 15 values, it will be seen that the result obtained must be very 
near the correct value for the rise between the given temperatures. It is then only 
necessary to multiply this rise in temperature by the thermal capacity, C, of the ball 
to find the quantity of heat that has passed along the wire in one minute, and the 
conductivity can be calculated from the formula 

„ cei 

is. = 



■in* (T - t) 60 

where r is the radius of the wire. 

In order to obtain an accmrate determination of the thermal capacity of the ball, I 
took it to Dublin, where the capacity was most carefully determined for me, during 
the time I was there, by Dr. John Joly, F.R.S., by his most ingenious steam 
calorimeter method." I have to thank Dr. Joly for the trouble to which he put 
himself in making the determination. 

As the most important thing in testing the method is to show that with different 
lengths the resulting determination of the conductivity remains practically the same, 
these series of tests and the results will be given first. 

The wire first used was what was called six years ago high electrical conductivity 
copper. The diameter was 2 - l millims., density 8*85, volume specific (electrical) 
resistance, 1834 in electromagnetic units. This wire was almost exclusively used, 
but in the course of the work tests were made of wire got from Messrs. Glover and 
Co. in the end of the year 1890. Messrs. Glover's wire was found to have con- 
siderably higher conductivity, both electrically and thermally, than the first- 
mentioned wire, which for convenience will be called the laboratory copper, as it was 
what was used for all the electrical work in the laboratory. Taking the laboratory 
wire as 100 per cent, conductivity (thermally and electrically), it was found that 
Messrs. Glover's wire was 106 "6 per cent, electrical, and 108 per cent, thermal con- 
ductivity. 

These results will be referred to further on (p. 180). They are merely mentioned 
here to show that the best conducting- wire was not used for the exhaustive tests. 

Table II. shows the record of series of experiments made on laboratory copper wire. 
The wire was soldered into the heating box and ball as described ; an experiment 
was made and the length measured carefully. The ball was then heated by a blow- 

* J. Jolt, 'Roy. Soo. Proc.,' vol. 41, p. 352, 1886. 



THE THERMAL CONDUCTIVITY OP METALS. 



177 



pipe flame to allow the wire to be taken out. A short piece was then cut off and the 
shortened wire again soldered into the ball. 



Table II. — Showing rise of Temperature of Calorimeter Ball with time. 
Diameter of wire = "210 centim. Temperature readings taken every half-minute. 



Length 
=6'31 centims. 


Length 
= 5-87 centims. 


Length 
=5-23 C. 


Length 
= 4'39 centims. 


Length 
= 4'01 centims. 


Temp, reading at 
every half-minute. 


Temp, reading at 
ever}' half- minute. 


Temp, reading at 
every half-minute. 


Temp, reading at 
every half-minute. 


Temp, reading at 
every half-minute. 


°c. 


C. 


°C. 


°C. 


°C. 


6-45 


6-25 


7-0 


6-05 


7-35 


6-65 


6-45 


7-25 


695 


7-7 


6 85 


67 


7-5 


7-2 


8-0 


7-05 


6-9 


775 


7-45 


83 


7-25 


71 


8-0 


7-7 


8-6 


745 


7-3 


8-2 


80 


8-95 


765 


7-5 


8-4 


8-25 


9-25 


7-85 


7-75 


8-65 


8-5 


9-55 


805 


795 


8-85 


8 75 


9-85 


8-25 


8-2 


91 


9-05 


10-15 


8-45 


8-4 


9-35 


9-3 


10-40 


8-65 


8-6 


9-55 


9-6 


10-75 


8-85 


8-8 


9-8 


9-85 


1105 


905 


9-0 


10-0 


10-1 


11-36 


9-2 


9-2 


10-2 


1035 


11-65 


9-4 


9-4 


10-4 


10-6 


11-9 


9-55 


9-6 


10-65 


10-8 


12-2 


9-75 


9-8 


10-85 


10-05 


12-5 


9-95 


10-0 


11-05 


11-3 


12-75 


101 


1015 


11-25 


11-5 


13-0 


103 


10-35 


11-45 


11-75 


13-25 


10-45 


10-55 


11-65 


12-0 


135 


10-65 


10-75 


12-1 


12-25 


13-8 


10-85 


10-9 


12-3 


12-45 


14 05 


10-95 


11 1 


12-5 


12-7 


143 


11T5 


11-25 


12-7 


12-95 


14-55 


11-3 


11-45 


129 


1315 


14-8 


11-45 


11-65 


13-05 


13-35 


15-1 


11-6 


11-8 


13-25 


1356 


15-35 


11-8 


120 




13-8 


15-6 


11-95 


1215 




14-0 


15-85 


121 


12-35 




14-25 


161 


12-25 


12-55 




14-45 


168 


12-4 








16-55 


12-6 








168 


12-75 










12-9 










]305 










Temp.ofair9°-85C. 

Temp, of hot water 

97°-3 C. 


Temp, of air 9°T C. 

Temp, of hot water 

97°-0 C. 


Temp, of air 10°-0 C. 

Temp, of hot water 

97°-0 C. 


Temp.ofairlO°-35C. 

Temp, of hot water 

96-4° C. 


Temp.ofairl2°-3C. 

Temp, of hot water 

96°-7 C. 



MDCCCXCV. — A. 



2 A 



178 



MR. J. H. GRAY ON A METHOD OF DETERMINING 




*pou6-ifu?d -sjniiki&fuia^ 



THE THERMAL CONDUCTIVITY OF METALS. 



179 



The temperature of the hot water varied not more than half a degree during an 
experiment, and the value given in each column of the preceding Table is the mean 
throughout the time. The columns of temperatures were, immediately after an 
experiment, put on a curve with time as abscissse. The effect of radiation to and 
from the calorimeter ball is fairly well marked. At the point corresponding to the 
temperature of the air in each curve there is an increase of curvature, caused by the 
fact that the radiation has changed from negative to positive. 

In order to find the flow of heat, the rise of temperature per minute was read from 
the curve at- a temperature x° below that of the air, and this was added to the rise 
for x° above that of the air. x varied from 0° to 4° or 5°. By this means from ten 
to fifteen readings were got, and the mean of these gave the rise at the temperature 
of the air. 

For example, for the length 6*31 centims. in the first column of Table I, the rise 

thus obtained from the curve, Diagram I., was '3605 in one minute. The capacity 

of the ball and of the part of the thermometer with the water in the hole was found 

to be 68-9. 

There 

68-9 x -3605 x 6-31 



K = 



it x (-105) 2 x S7-45 x 60 
•883 C.G.S. unit, 



This value is not corrected for the error given by the approximate formula already 
mentioned. 

Error 

a K b — a 
W 1: V 



(V, - 6) - 



1 + - 



a K J- a 



2/ h 



= '69° in this case. 



This makes the difference of temperature less by '7°, and when this correction is 
made we get for the conductivity "889 C.G.S. unit. The conductivity as calculated 
from five different lengths becomes, after the correction is made — 



Length in centims. 


Conductivity. 


6-31 

5-87 
523 
4-59 
4-015 


■889 
■893 
■890 
•887 
•883 



The greatest difference between these values is a little over 1 per cent. Taking 

2 A 2 



180 



MR. J. H. GRAY ON A METHOD OF DETERMINING 



their mean, we get for the thermal conductivity of the laboratory copper wire 
•8884 C.G.S. unit. This value is the mean conductivity between the temperatures 
97° C. and 10° C. 

The following Table gives the results of a series of tests on another portion of the 
same wire : — 



Length in centinis. 


Conductivity. 


611 

5-71 

4-80 
4-43 


•888 
•883 
•892 
•889 



The mean of these values is 
the preceding series. 

Taking Angstrom's formula, 



S80, being ■£$ per cent, less than that obtained from 



K = 1-027 (1 — -002140, 



and finding K for 53°, which is the mean of 97° and 10°, we get K = "9208 C.G.S. 
unit. 

The close agreement in the values obtained with different lengths shows that the 
errors already mentioned as possible are practically eliminated. Angstrom's value is 
4'5 per cent, greater than "8884, but, as has been mentioned (p. 176), the conductivity 
of the laboratory copper wire is 8 per cent, less than that of Glover's wire afterwards 
tested. In a previous paper, Angstrom gives "91 as the value for 5l'3° C. 

In a paper read before the Royal Society last year, Dr. R. W. Stewart, using the 
Forbes method, but substituting a single thermo-electric junction for the thermometers, 
gives the values for copper and iron. At the temperature 53° C he gets for copper 
K = l - 067, which is 10 per cent, higher than the value obtained for any specimen of 
copper tested in the present investigation. 

The conductivity of the wire obtained from Messrs. Glover and Son was found to 
be - 9594 C.G.S. This was the best conducting copper tested by the present method. 
The specific electrical resistance was 1730 in absolute units. 

To test separately the effect of any alterations, separate experiments were made. 

I. Instead of enclosing the whole length of the wire (laboratory copper) in a tube, 
only a part was enclosed. 

The paper tube was shortened by 2 or 3 millims. each time, and the conductivity 
of the same length of wire was determined after each shortening of the tube. The 
result found was, that the shortening (which was, of course, done from the cool end of 
the wire) had practically no effect on the value so long as it was arranged that there 
were no draughts of cold air. If for no other reason, the paper tube is necessary to 



THE THERMAL CONDUCTIVITY OF METALS. 181 

prevent draughts, as the latter make a determination impossible. It was found that 
the paper tube could be shortened as much as to leave the lower half of the wire 
exposed without any appreciable diminution of the value obtained. When it was 
shortened much further, the value began to diminish till, when the tube was removed 
altogether, the value obtained was found to be fully fi per cent, lower than when the 
tube completely covered the wire. When the wire was bare it was found very 
difficult to prevent draughts caused by the hot wire, and these draughts made the 
readings of the thermometer very irregular. 

In connection with this, it will be noted that there is a particular advantage 
in having the calorimeter ball lower in position than the heating box, as the hot air 
round the latter rises, and so does not affect the water-jacket. It has been suggested, 
however, that a separate experiment should be made to test whether any heat reached 
the ball otherwise than through the wire. For this purpose the ball was suspended 
by silk threads, in such a way that its highest point was 4"4 centimetres from 
the bottom of the heating box. The water jacket was placed round the ball, and the 
sheets of paper put on the top of the jacket. The water in the heating box was kept 
boiling for twenty-five minutes, and the temperature of the ball, as indicated by the 
thermometer in it, was noted at intervals. No change in the thermometer reading 
could be detected, although -j^th of one degree can be read without difficulty on the 
thermometer scale. 

As a further test of the effect of the paper tube, the upper half length of the wire 
which was being tested, was left unprotected by any tube, while the lower half was 
enclosed. The result was practically the same as if there had been no tube at all. 

In order to make certain that the thermometer in the hot water indicated the 
temperature of the upper end of the wire, a thermo-electric junction was used. The 
junction was made of very thin wires of copper and platinoid, and, after being wrapped 
once round the hot end of the wire just at the end, was soldered there. The other 
junction was fixed to a thermometer and immersed in water. The heating box was 
then filled with water, which was kept boiling. The water in the vessel containing 
the other junction was gradually heated up till there was no deflection in the mirror 
galvanometer used. Both junctions must then be at the same temperature. When 
there was no deflection in the galvanometer the thermometers were found to be 
indicating the same temperatures. 

Several qualities of copper were tested, the results of which are given below. 

Copper wire, made by Messrs. Bolton and Co., Cheadle. This wire was by 
mistake sent away before its electrical conductivity was measured, and it cannot be 
got again. 



182 



MB, J. H. GRAY ON A METHOD OF DETERMINING 



Length used (in centims.). 


Mean conductivity between 
10° C. and 97° C. 


7-0 
633 
5-7 
51 


■867 
■862 
•859 
■858 



The greatest variation here is 1 per cent., and the mean value is '8612. 
Some specimens of copper wire were bought in a plumber's shop, of quality used for 
bell-hanging. 



Specimen. 


Diameter 
(in centims.). 


Specific resistance 
(electrical). 


Mean thermal 
conductivity. 


1 
2 


•200 
•204 


5545 
4701 


•3198 
•3497 



Conductivity of Laboratory wire 
Conductivity of Specimen 1 

Conductivity of Laboratory wire 
Conductivity of Specimen 2 



Conductivity of Glover's wire 
Conductivity of Laboratory wire 



= 278 for heat, 

= 2 "8 6 for electricity. 

= 2 '54 for heat, 

= 2 '5 6 for electricity. 

= 1-08 for heat, 

= T066 for electricity. 



In all the wires tested it was found that if one metal was a better conductor for 
electricity it was also better for heat. This has been noticed by several investigators, 
notably Professor Tait, and Wiedemann and Franz. Beyond this the present 
results cannot go, as enough trials were not made to allow of comparison. Previous 
experimenters have found that the ratio of electrical conductivities of two wires is 
not exactly equal to the ratio of thermal conductivities. This is indeed to be 
expected, if the coefficients already obtained for the alteration with temperature are 
accurate. For example, in copper the coefficient of variation per degree for electrical 
conductivity is very much greater than that found for thermal conductivity, so that, 
even if the ratios were equal at one temperature, they must be unequal at all other 
temperatures. In some of the wires tested the electrical and thermal ratios differed 
by as much as 4 or 5 per cent. 

Before the present investigation, the absolute values for the conductivity of the 



THE THERMAL CONDUCTIVITY OF METALS. 



183 



more expensive metals had not been determined, although relative values had been 
found by Wiedemann and Franz.* 

I am very much indebted to Messrs. Johnson, Matthey, and Co. for their great 
kindness in preparing and lending to me wires of gold, platinum, silver, and other 
pure metals, of 2 millims. diameter, and of such a length as to enable me to measure 
without difficulty both the thermal and electrical conductivities. 

Unfortunately, I cannot find a record of the value obtained for the electrical 
conductivity of the gold wire, and it has been returned some time ago. As, however, 
Messrs. Johnson, Matthey, and Co. stated, when sending it, that it was as pure as 
could be made, it will perhaps be sufficient for me to use the value that has already 
been found for the electrical conductivity of gold as determined by other experi- 
menters. 

The curves for the calculation of the conductivity of silver wire are shown in 
Diagram II. The values for the different lengths are given below. 

Silver Wire. 



Length. 


Thermal conductivity in 

C.G.S. units between 

15° C. and 98° 0. 


7-86 
6-59 
6-59 
5-61 


•956 

■960 
•963 
•973 



It will be observed that the second and third values, although for the same length, 
differ by about §• per cent. They are both given however, as they agree within the 
limits of observational errors. The mean of these values is "9G28. 

As the curves for gold and platinum are very similar to those for copper and silver, 
it may be enough to give the values obtained for their conductivities. 

Gold Wire (not annealed). Diameter = "202 centim. 



Thermal conductivity in 
C.G.S. unit. 


Electrical resistance as 

determined by 

Dr. Matthiessen. 


•7464 


2188 



Comparing these values with those for Messrs. Glover's copper, which was found 
to be '959, we find that the thermal conductivity of gold is 78 per cent, and the 
electrical conductivity 81 "6 per cent, that of copper. 

* 'Annales de Chemie,' vol. 41, p. 107, 1854. 



184 



MR, J. H. GRAY ON A METHOD OP DETERMINING 













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THE THERMAL CONDUCTIVITY OF METALS. 
Platinum Wire (not annealed). Diameter = "202 centim. 



185 



Thermal conductivity. 



Electrical resistance. 



■1861 



9180 



Here the thermal and electrical conductivities are each 19 per cent, of the 
conductivity of copper. 

The gold, platinum, and silver were afterwards carefully annealed by Messrs. 
Johnson, Matthey, and Co., and the conductivities again determined. In each of 
the cases the alteration due to annealing was less than 1 per cent, both in electrical 
and thermal conductivity. 

The results for the different metals are therefore — 

Mean Conductivity between Temperatures 10° C. and 97° C. 



o 
Very f „ 4 

Gold 

Platinum 


•9594 
•8884 
•8612 
•3497 
•3198 
■9628 
•7464 
T861 


Diameter. 


millims. 
2-00 
211 
3-09 
2-04 
2-04 
2-02 
2-00 
2-00 





It is intended to use other liquids than boiling water to heat one end of the wire, and 
in this way test the alteration of conductivity with temperature. Up to the present 
time no alloys have been tested, but it is intended that tests should be made of some, 
such as platinoid and German silver ; also iron, as pure as possible, might be tested. 

Instead of boiling water, steam was used for some time in this investigation, and 
was in some respects found to be more convenient. Fig. 7 is a sketch showing a 
section through the middle of the apparatus. 

The steam is generated in the vessel W, passes along the upper tube T in the 
direction of the arrows, and blows directly on the end of the wire, afterwards passing 
out through the outside copper tube P, and escaping by the outlet B. 

The thermometer D indicates the temperature of the steam just when it strikes the 
wire. It will be seen that the outer tube with the steam in it serves as a steam 
jacket, and thus keeps the steam in the inner tube T at a high temperature. The 
sloping bottom where the wire is fixed at A is so made to prevent water accumulating 
there. To ensure that as much steam as will supply all the heat that the copper can 
take up is impinging at A, it is only necessary to arrange that the steam emerges at 
B as steam. 

JIDCCCXCV. — A. 2 B 



186 MR. J. H. GRAY ON THE THERMAL CONDUCTIVITY OF METALS. 

Fig. 7. 




The outside tube need not be more than 4 centims. diameter, and may be round, but 
the part where the wire is soldered in must be thickened and made as shown in the 
sketch, so that there may be no risk of water gathering above the wire. The length 
of the tube need not exceed 15 centims. This allows sufficient length for the tube to 
be inserted into the screen, which prevents the heat of the lamp from altering the 
temperature of the ball. The diameter of the inside tube may be 1*5 centims. With 
this apparatus most satisfactory results were obtained. 

When a metal is tested for the first time, it will be advisable to find its approxi- 
mate thermal conductivity by compai'ing its electrical conductivity with copper. This 
will give an idea as to which calorimeter ball to use, and what length of wire will give 
a convenient rise of temperature per minute. A test is then almost as simple as for 
electrical conductivity. 



\ 



[ 187 ] 



VI. Argon, a Netv Constituent of the Atmosphere. 
By Lord Rayleigh, Sec. R.S., and Professor William Ramsay, F.R.S. 

Received and Read January 31, 1895. 

"Modern discoveries have not been made by large collections of facts, with subsequent discussion, 
separation, and resulting deduction of a truth thus rendered perceptible. A few facts have suggested an 
hypothesis, which means a supposition, proper to explain them. The necessary results of this supposition 
are worked out, and then, and not till then, other facts are examined to see if their ulterior results are 
found in Nature." — De Moegan, " A Budget of Paradoxes," ed. 1872, p. 55. 

1. Density of Nitrogen from Furious Sources. 

In a former paper 4 ' it has been shown that nitrogen extracted from chemical 
compounds is about one-half per cent, lighter than " atmospheric nitrogen." 

The mean numbers for the weights of gas contained in the globe used were as 
follows : — 

grams. 

From nitric oxide 2*3001 

From nitrous oxide 2*2990 

From ammonium nitrite .... 2*2987 

while for " atmospheric" nitrogen there was found — 

By hot copper, 1892 2-3103 

By hot iron, 1893 2-3100 

By ferrous hydrate, 1894 . . . 2*3102 

At the suggestion of Professor Thoepe, experiments were subsequently tried with 
nitrogen liberated from urea by the action of sodium hypobromite. The cax*bon and 
hydrogen of the urea are supposed to be oxidized by the reaction to C0 2 and H 3 0, 
the former of which would be retained by the large excess of alkali employed. It 
was accordingly hoped that the gas would require no further purification than drying. 
If it proved to be light, it would at any rate be free from the suspicion of containing 
hydrogen. 

* Rayleigh, "On an Anomaly encountered in Determinations of the Density of Nitrogen Gas," 
1 Proc. Roy. Soc.,' vol. 55, p. 340, 1894. 

MDCCCXCV. — A. 2 B 2 27.6.95. 



L38 LORD RAYLEIGH AND PROFESSOR W. RAMSAY ON ARGON, 

The hjpobromite was prepared from commercial materials in the proportions 
lecommended for the analysis of urea — 100 grams, caustic soda, 250 cub. centims. 
water, and 25 cub. centims. of bromine. For our purpose about one and a half times 
the above quantities were required. The gas was liberated in a bottle of about 
900 cub. centims. capacity, in which a vacuum was first established. The full quan- 
tity of hypobromite solution was allowed to run in slowly, so that any dissolved gas 
might be at once disengaged. The urea was then fed in, at first in a dilute condition, 
but, as the pressure rose, in a 10 per cent, solution. The washing out of the 
apparatus, being effected with gas in a highly rarefied state, made but a slight 
demand upon the materials. The reaction was well under control, and the gas could 
be liberated as slowly as desired. 

In the first experiment, the gas was submitted to no other treatment than slow 
passage through potash and phosphoric anhydride, but it soon became apparent that 
the nitrogen was contaminated. The "inert and inodorous" gas attacked vigorously 
the rnercury of the Topler pump, and was described as smelling like a dead rat. As 
to the weight, it proved to be in excess even of the weight of atmospheric nitrogen. 

The corrosion of the mercury and the evil smell were in great degree obviated by 
passing the gas over hot metals. For the fillings of June 6, 9, 13, the gas passed 
through a short length of tube containing copper in the form of fine wire, heated by 
a flat Bunsen burner, then through the furnace over red-hot iron, and back over 
copper oxide. On June 19 the furnace tubes were omitted, the gas being treated 
with the red-hot copper only. The results, reduced so as to correspond with those 
above quoted, were — 

June 6 2-2978 

„ 9 2-2987 

„1.3 2-2982 

„ 19 2-2994 

Mean .... 2"2985 

Without using heat it has not been found possible to prevent the corrosion of the 
mercury. Even when no urea is employed, and air simply bubbled through the hypo- 
bromite solution is allowed to pass with constant shaking over mercury contained in 
a U tube, the surface of the metal was soon fouled. When hypochlorite was 
substituted for hypobromite in the last experiment there was a decided improvement, 
and it was thought desirable to try whether the gas prepared from hypochlorite and 
urea would be pure on simple desiccation. A filling on June 25 gave as the weight 
2'3343, showing an excess of 36 mgs., as compared with other chemical nitrogen, and 
of about 25 mgs. as compared with atmospheric nitrogen. A test with alkaline 
pyrogallate appeared to prove the absence from this gas of free oxygen, and only a 
trace of carbon could be detected when a considerable quantity of the gas was passed 
over red-hot cupric oxide into solution of baryta. 



A NEW CONSTITUENT OF THE ATMOSPHERE. 189 

Although the results relating to urea nitrogen are interesting for comparison with 
that obtained from other nitrogen compounds, the original object was not attained on 
account of the necessity of retaining the treatment with hot metals. We have found, 
however, that nitrogen from ammonium nitrite may be prepared without the employ- 
ment of hot tubes, whose weight agrees with that above quoted. It is true that the 
gas smells slightly of ammonia, easily removable by sulphuric acid, and apparently 
also of oxides of nitrogen. The solution of potassium nitrite and ammonium chloride 
was heated in a water-bath, of which the temperature rose to the boiling-point only 
towards the close of operations. In the earlier stages the temperature required 
careful watching in order to prevent the decomposition taking place too rapidly. The 
gas was washed with sulphuric acid, and after passing a Nessler test, was finally 
treated with potash and phosphoric anhydride in the usual way. The following results 
have been obtained : — 

July 4 2-2983 

9 2-2989 

„ 13 2-2990 

Mean .... 2*2987 

It will be seen that in spite of the slight nitrous smell there is no appreciable differ- 
ence in the densities of gas prepared from ammonium nitrite with and without the 
treatment by hot metals. The result is interesting, as showing that the agreement 
of numbers obtained for chemical nitrogen does not depend upon the use of a red 
heat in the process of purification. 

The five results obtained in more or less distinct ways for chemical nitrogen stand 
thus : — 

From nitric oxide 2'3001 

From nitrous oxide 2 - 2990 

From ammonium nitrite purified at a red heat .... 2 - 2987 

From urea 2*2985 

From ammonium nitrite purified in the cold 2 -2987 

Mean 2-2990 

These numbers, as well as those above quoted for "atmospheric nitrogen," are subject 
to a correction (additive)* of '0006 for the shrinkage of the globe when exhausted.t If 
they are then multiplied in the ratio of 2*3108 : 1*2572, they will express the weights 
of the gas in grams, per litre. Thus, as regards the mean numbers, we find as the 
weight per litre under standard conditions of chemical nitrogen 1*2511, that of 
atmospheric nitrogen being 1*2572. 

[* In the Abstract of this paper (' Proc. Roy. Soc.,' vol. 57, p. 265) the correction of '0006 was 
erroneously treated as a deduction. — April, 1895.] 

t Ratleigh, " On the Densities of the Principal Gases," ' Proc. Roy. Soc.,' vol. 53, p. 134, 1893. 



190 LORD RAYLEIGH AND PROFESSOR W. RAMSAY ON ARGON, 

It is of interest to compare the density of nitrogen obtained from chemical com- 
pounds with that of oxygen. We have N 3 : 2 = 2*2996 : 2'6276 = 0-87517 ; so that 
if 3 = 16, N 2 = 14 , 003. Thus, when the comparison is with chemical nitrogen, 
the ratio is very nearly that of 16 : 14. But if "atmospheric nitrogen" be substituted, 
the ratio of small integers is widely departed from. 

The determination by Stas of the atomic weight of nitrogen from synthesis of 
silver nitrate is probably the most trustworthy, inasmuch as the atomic weight of 
silver was determined with reference to oxygen with the greatest care, and oxygen is 
assumed to have the atomic weight 16. If, as found by Stas, AgN0 3 :Ag= 1 "574 90:1, 
and Ag : = 107-930 : 16, then N : O = 14"049 : 16. 

To the above list may be added nitrogen, prepared in yet another manner, whose 
weight has been determined subsequently to the isolation of the new dense constituent 
of the atmosphere. In this case nitrogen was actually extracted from air by means 
of magnesium. The nitrogen thus separated was then converted into ammonia by 
action of water upon the magnesium nitride, and afterwards liberated in the free 
state by means of calcium hypochlorite. The purification was conducted in the usual 
way, and included passage over red-hot copper and copper oxide. The following was 
the result : — 

Globe empty, October 30, November 5 2-82313 

Globe full, October 31 . . -52395 

Weight of gas 2-29918 

It, differs inappreciably from the mean of other results, viz., 2'2990, and is of 
special interest as relating to gas which, at one stage of its history, formed part of 
the atmosphere. 

Another determination with a different apparatus of the density of " chemical " 
nitrogen from the same source, magnesium nitride, which had been prepared by 
passing " atmospheric " nitrogen over ignited magnesium, may here be recorded. The 
sample differed from that previously mentioned, inasmuch as it had not been 
subjected to treatment with red-hot copper. After treating the nitride with water, 
the resulting ammonia was distilled off, and collected in hydrochloric acid ; the 
solution was evaporated to dryness ; the dry ammonium chloride was dissolved in 
water, and its concentrated solution added to a freshly prepared solution of sodium 
hypobromite. The nitrogen was collected in a gas-holder over water which had 
previously been boiled, so as at all events partially to expel air. The nitrogen passed 
into the vacuous globe through a solution of potassium hydroxide, and through two 
drying-tubes, one containing soda-lime, and the other phosphoric anhydride. 

At 18*38° C, and 754 - 4 mgs. pressure, 162*843 cub. centims. of this nitrogen 
weighed 0*18963 gram. Hence :— 

Weight of 1 litre at 0° C. and 760 millims. pressure . . . 1-2521 gram. 



A NEW CONSTITUENT OF THE ATMOSPHERE. 191 

The mean result of the weight of 1 litre of " chemical " nitrogen has been found 
to equal 1*2511. It is therefore seen that ■'chemical" nitrogen, derived from 
*' atmospheric " nitrogen, without any exposure to red-hot copper, possesses the 
usual density. 

Experiments were also made, which had for their object to prove that the ammonia, 
produced from the magnesium nitride, is identical with ordinary ammonia, and 
contains no other compound of a basic character. For this purpose, the ammonia 
was converted into ammonium chloride, and the percentage of chlorine determined 
by titration with a solution of silver nitrate which had been standardized by titrating 
a specimen of pure sublimed ammonium chloride. The silver solution was of such a 
strength that 1 cubic centim. precipitated the chlorine from 0*001701 gram, of 
ammonium chloride. 

1. Ammonium chloride from orange-coloured sample of magnesium nitride. 
0*1106 gram, required 43*10 cub. centims. of silver nitrate = 66*35 per cent, of 

chlorine. 

2. Ammonium chloride from blackish magnesium nitride. 

0*1118 gram, required 43*6 cub. centims. of silver nitrate = 66*35 per cent, of 
chlorine. 

3. Ammonium chloride from nitride containing a large amount of una/ttacked 
magnesium. 

0*0630 gram, required 24*55 cub. centims. of silver nitrate = 66*30 per cent, of 
chlorine. 

Taking for the atomic weights of hydrogen, H = 1*0032, of nitrogen, N = 14*04, 
and of chlorine, CI = 35*46, the theoretical amount of chlorine in ammonium chloride 
is 66*27 per cent. 

From these results — that nitrogen prepared from magnesium nitride obtained by 
passing " atmospheric " nitrogen over red-hot magnesium has the density of 
"chemical" nitrogen, and that ammonium chloride prepared from magnesium nitride 
contains practically the same percentage of chlorine as pure ammonium chloride— it 
may be concluded that red-hot magnesium withdraws from " atmospheric " nitrogen 
no substance other than nitrogen capable of forming a basic compound with hydrogen. 

In a subsequent part of this paper, attention will again be called to this 
statement. (See addendum p. 240.) 

2. Reasons for Suspecting a hitherto Undiscovered Constituent in Air. 

When the discrepancy of weights was first encountered, attempts were naturally 
made to explain it by contamination with known impurities. Of these the most 
likely appeared to be hydrogen, present in the lighter gas, in spite of the passage over 
red-hot cupric oxide. But, inasmuch as the intentional introduction of hydrogen 
into the heavier gas, afterwards treated in the same way with cupric oxide, had no 
effect upon its weight, this explanation had to be abandoned ; and, finally, it became 



192 LORD RAYLEIGH AND PROFESSOR W. RAMSAY ON ARGON, 

clear that the difference could not be accounted for by the presence of any known 
impurity. At this stage it seemed not improbable that the lightness of the gas 
extracted from chemical compounds was to be explained by partial dissociation of 
nitrogen molecules N 3 into detached atoms. In order to test this suggestion, both 
kinds of gas were submitted to the action of the silent electric discharge, with the 
result that both retained their weights unaltered. This was discouraging, and a 
further experiment pointed still more markedly in the negative direction. The 
chemical behaviour of nitrogen is such as to suggest that dissociated atoms would 
possess a higher degree of activity, and that, even though they might be formed in 
the first instance, their life would probably be short. On standing, they might be 
expected to disappear, in partial analogy with the known behaviour of ozone. With 
this idea in view, a sample of chemically-prepared nitrogen was stored for eight 
months. But, at the end of this time, the density showed no sign of increase, 
remaining exactly as at first.* 

Regarding it as established that one or other of the gases must be a mixture, 
containing, as the case might be, an ingredient much heavier or much lighter than 
ordinary nitrogen, we had to consider the relative probabilities of the various possible 
interpretations. Except upon the already discredited hypothesis of dissociation, it 
was difficult to see how the gas of chemical origin could be a mixture. To suppose 
this would be to admit two kinds of nitric acid, hardly reconcilable with the work of 
Stas and others upon the atomic weight of that substance. The simplest explanation 
in many respects was to admit the existence of a second ingredient in air from which 
oxygen, moisture, and carbonic anhydride had already been removed. The pro- 
portional amount required was not great. If the density of the supposed gas were 
double that of nitrogen, one-half per cent, only by volume would be needed ; or, if the 
density were but half as much again as that of nitrogen, then one per cent, would 
still suffice. But in accepting this explanation, even provisionally, we had to face the 
improbability that a gas surrounding us on all sides, and present in enormous 
quantities, could have remained so long unsuspected. 

The method of most universal application by which to test whether a gas is pure or 
a mixture of components of different densities is that of diffusion. By this means 
Graham succeeded in effecting a partial separation of the nitrogen and oxygen of the 
air, in spite of the comparatively small difference of densities. If the atmosphere 
contain an unknown gas of anything like the density supposed, it should be possible 
to prove the fact by operations conducted upon air which had undergone atmolysis. 
If, for example, the parts least disposed to penetrate porous walls were retained, the 
" nitrogen " derived from it by the usual processes should be heavier than that 
derived in like manner from unprepared air. This experiment, although in view from 
the first, was not executed until a later stage of the inquiry (§ 6), when results were 

* Rayleigh, ' Proc. Rot. Soc.,' vol. 55, p. 344, 1894. 



A NEW CONSTITUENT OP THE ATMOSPHERE. 193 

obtained sufficient of themselves to prove that the atmosphere contains a previously 
unknown gas. 

But although the method of diffusion was capable of deciding the main, or at any 
rate the first question, it held out no prospect of isolating the new constituent of the 
atmosphere, and we therefore turned our attention in the first instance to the con- 
sideration of methods more strictly chemical. And here the question forced itself 
upon us as to what really was the evidence in favour of the prevalent doctrine that 
the inert residue from air after withdrawal of oxygen, water, and carbonic anhydride, 
is all of one kind. 

The identification of " phlogisticated ah" '"' with the constituent of nitric acid is due 
to Cavexdish, whose method consisted in operating with electric sparks upon a short 
column of gas confined with potash over mercury at the upper end of an inverted 
U-tube.* This tube (M) was only about yg- inch in diameter, and the column of 
gas was usually about 1 inch in length. After describing some preliminary trials, 
Cavendish proceeds : — " I introduced into the tube a little soap-lees (potash), and then 
let up some dephlogisticatedt and common air, mixed in the above mentioned 
proportions which rising to the top of the tube M, divided the soap-lees into its two 
legs. As fast as the air was diminished by the electric spark, I continued adding more 
of the same kind, till no further diminution took place : after which a little pure dephlo- 
gisticated air, and after that a little common air, were added, in order to see whether 
the cessation of diminution was not owing to some imperfection in the proportion of 
the two kinds of air to each other ; but without effect. The soap-lees being then 
poured out of the tube, and separated from the quicksilver, seemed to be perfectly 
neutralised, and they did not at all discolour paper tinged with the juice of blue 
flowers. Being evaporated to dryness, they left a small quantity of salt, which was 
evidently nitre, as appeared by the manner in which paper, impregnated with a 
solution of it, burned." 

Attempts to repeat Cavendish's experiment in Cavendish's manner have only 
increased the admiration with which we regard this wonderful investigation. 
"Working on almost microscopical quantities of material, and by operations extending 
over days and weeks, he thus established one of the most important facts in 
chemistry. And what is still more to the purpose, he raises as distinctly as we 

* "Experiments on Air," 'Phil. TraDs.,' vol. 75, p. 372, 1785. 

[t The explanation of combustion in Cavendish's day was still vague. It was generally imagined 
that substances capable of burning contained an unknown principle, to which the name ' phlogiston ' 
was applied, and which escaped during combustion. Thus, metals and hydrogen and other gases were 
said to be ' phlogisticated ' if they were capable of burning in air. Oxygen being non-inflammable was 
named ' dephlogisticated air,' and nitrogen, because it was incapable of supporting combustion or life 
was named by Priestley ' phlogisticated air,' although up till Cavendish's time it had not been made to 
unite with oxygen. 

The term used for oxygen by Cavendish is ' dephlogisticated air,' and for nitrogen, ' phlogisticated 
air.'— April, 1895.] 

MDCCCXCV. — A. 2 C 



194 LORD RATLEIGH AND PROFESSOR W. RAMSAY ON ARGON, 

could do, and to a certain extent resolves, the question above suggested. . The 
passage is so important that it will be desirable to quote it at full length. 

" As far as the experiments hitherto published extend, we scarcely know more of 
the phlogisticated part of our atmosphere than that it is not diminished by lime- 
water, caustic alkalies, or nitrous air ; that it is unfit to support fire or maintain life 
in animals ; and that its specific gravity is not much less than that of common air ; 
so that, though the nitrous acid, by being united to phlogiston, is converted into air 
possessed of these properties, and consequently, though it was reasonable to suppose, 
that part at least of the phlogisticated air of the atmosphere consists of this acid 
united to phlogiston, yet it was fairly to be doubted whether the whole is of this 
kind, or whether there are not in reality many different substances confounded 
together by us under the name of phlogisticated air. I therefore made an experiment 
to determine whether the whole of a given portion of the phlogisticated air of the 
atmosphere could be reduced to nitrous acid, or whether there was not a part of a 
different nature to the rest which would refuse to undergo that change. The fore- 
going experiments indeed in some measure decided this point, as much the greatest 
part of the air let up into the tube lost its elasticity ; yet as some remained 
unabsorbed it did not appear for certain whether that was of the same nature as the 
rest or not. For this purpose I diminished a similar mixture of dephlogisticated and 
common air, in the same manner as before, till it was reduced to a small part of its 
original bulk. I then, in order to decompound as much as I could of the phlogisti- 
cated air which remained in the tube, added some dephlogisticated air to it and 
continued the spark until no further diminution took place. Having by these means 
condensed as much as I could of the phlogisticated air, I let up some solution of liver 
of sulphur to absorb the dephlogisticated air ; after which only a small bubble of air 
remained unabsorbed. which certainly was not more than y|-g- of the bulk of the 
phlogisticated air let up into the tube ; so that, if there is any part of the phlogisti- 
cated air of our atmosphere which differs from the rest, and cannot be reduced to 
nitrous acid, we may safely conclude that it is not more than ywo P ar ^ °f ^he w hole." 

Although Cavendish was satisfied with his result, and does not decide whether 
the small residue was genuine, our experiments about to be related render it not 
improbable that his residue was really of a different kind from the main bulk of the 
" phlogisticated air," and contained the gas now called argon. 

Cavendish gives data'" from which it is possible to determine the rate of absorption 
of the mixed gases in his experiment. The electrical machine used " was one of 
Mr. Nairne's patent machines, the cylinder of which is 12| inches long and 7 in 
diameter. A conductor, 5 feet long and 6 inches in diameter, was adapted to it, and 
the ball which received the spark was placed two or three inches from another ball, 
fixed to the end of the conductor. Now, when the machine worked well. Mr. Gilpin 
supposes he got about two or tfn-ee hundred sparks a minute, and the diminution of 

* ' Phil. Trans.,' vol. 78, p. 271, 1788. 



A NEW CONSTITUENT OF THE ATMOSPHERE. 195 

the air during the half hour which he continued working at a time varied in general 
from 40 to 120 measures, but was usually greatest when there was most air in the 
tube, provided the quantity was not so great as to prevent the spark from passing 
readily." The " measure " spoken of represents the volume of one grain of quicksilver, 
or - 0048 cub. centim., so that an absorption of one cub. centim. of mixed gas per hour 
was about the most favourable rate. Of the mixed gas about two-fifths would be 
nitrogen. 

3. Methods of Causing Free Nitrogen to Combine. 

The concord between the determinations of density of nitrogen obtained from 
sources other than the atmosphere, having made it at least probable that some heavier 
gas exists in the atmosphere, hitherto undetected, it became necessary to submit 
atmospheric nitrogen to examination, with a view of isolating, if possible, the unknown 
and overlooked constituent, or it might be constituents. 

Nitrogen, however, is an element which does not easily enter into direct combination 
with other elements ; but with certain elements, and under certain conditions, combi- 
nation may be induced. The elements which have been directly united to nitrogen 
are (a) boron, (6) silicon, (c) titanium, (d) lithium, (e) strontium and barium, 
(f) magnesium, (g) aluminium, (h) mercury, (i) manganese, (j) hydrogen, and 
(k) oxygen, the last two by help of an electrical discharge. 

(a.) Nitride of boron was prepared by Wohler and Deville* by heating amorphous 
boron to a white heat in a current of nitrogen. Experiments were made to test 
whether the reaction would take place in a tube of difficultly fusible glass ; but it was 
found that the combination took place at a bright red heat to only a small extent, 
and that the boron, which had been prepared by heating powdered boron oxide with 
magnesium dust, was only superficially attacked. Boron is, therefore, not a convenient 
absorbent for nitrogen. [M. Moissan informs us that the reputation it possesses is 
due to the fact that early experiments were made with boron which had been 
obtained by means of sodium, and which probably contained a boride of that metal. 
—April, 1895.] 

(b.) Nitride of silicon^ also requires for its formation a white heat, and complete 
union is difficult to bring about. Moreover, it is not easy to obtain large quantities 
of silicon. This method was therefore not attempted. 

(c.) Nitride of titanium is said to have been formed by Deville and Cabon,| by 
heating titanium to whiteness in a current of nitrogen. This process was not tried 
by us. As titanium has an unusual tendency to unite with nitrogen, it might, 
perhaps, be worth while to set the element free in presence of atmospheric nitrogen, 
with a view to the absorption of the nitrogen. This has, in effect, been already done 

* ' Annales de Cliimie,' (3), 52, p. 82. 
t Schtjtzenbeegee, ' Comptes Rendus,' 89, 644. 
J ' Annalen der Chemie u. Pharmacie,' 101, H60. 
2 C 2 



196 LOED RATLEIGH AND PROFESSOR W. RAMSAY ON ARGON, 

by "Wohler and Deville ;* they passed a mixture of the vapour of titanium chloride 
and nitrogen over red-hot aluminium, and obtained a large yield of nitride. It is 
possible that a mixture of the precipitated oxide of titanium with magnesium dust 
might be an effective absorbing agent at a comparatively low temperature. [Since 
writing the above we have been informed by M. Moissan that titanium, heated to 
800°, burns brilliantly in a current of nitrogen. It might therefore be used with 
advantage to remove nitrogen from air, inasmuch as we have found that it does not 
combine with argon. — April, 1895.] 

(cl.), (e.) Lithium at a dull red heat absorbs nitrogen,t but the difficulty of 
obtaining the metal in quantity precludes its application. On the other hand, 
strontium and barium, prepared by electrolysing solutions of their chlorides in 
contact with mercury, and subsequently removing the mercury by distillation, are 
said by M AQUENisrE J to absorb nitrogen with readiness. Although we have not tried 
these metals for removing nitrogen, still our experience with their amalgams has led 
us to doubt their efficacy, for it is extremely difficult to free them from mercury by 
distillation, and the product is a fused ingot, exposing very little surface to the action 
of the gas. The process might, however, be worth a trial. 

Barium is the efficient absorbent for nitrogen when a mixture of barium carbonate 
and carbon is ignited in a current of nitrogen, yielding cyanide. Experiments have 
shown, however, that the formation of cyanides takes place much more readily and 
abundantly at a high temperature, a temperature not easily reached with laboratory 
appliances. Should the process ever come to be worked on a large scale, the gas 
rejected by the barium will undoubtedly prove a most convenient source of argon. 

(f.) Nitride of magnesium was prepared by Deville and Caron (Joe. cit.) during 
the distillation of impure magnesium. It has been more carefully investigated by 
Briegleb and Geuther,§ who obtained it by igniting metallic magnesium in a 
current of nitrogen. It forms an orange-brown, friable substauce, very porous, and 
it is easily produced at a bright red heat. When magnesium, preferably in the form 
of thin turnings, is heated in a combustion tube in a current of nitrogen, the tube is 
attacked superficially, a coating of magnesium silicide being formed. As the temperature 
rises to bright redness, the magnesium begins to glow brightly, and combustion takes 
place, beginning at that end of the tube through which the gas is introduced. The 
combustion proceeds regularly, the glow extending down the tube, until all the metal 
has united with nitrogen. The heat developed by the combination is considerable, 
and the glass softens ; but by careful attention and regulation of the rate of the 
current, the tube lasts out an operation. A piece of combustion tubing of the usual 
length for organic analysis packed tightly with magnesium turnings, and containing 

* ' Annalen der Chemie u. Pharmacie,' 73, 34. 
f Oitveaed, ' Comptes Rendus,' 114, 120. 
J Ouvrakd, ' Comptes Rendus,' 114, 25, and 220. 
§ ' Annalen der Cheniie u. Pharmacie,' 123, 228. 



A NEW CONSTITUENT OF THE ATMOSPHERE. 197 

about 30 grams, absorbs between seven and eight litres of nitrogen. It is essential 
that oxygen be excluded from the tube, otherwise a fusible substance is produced, 
possibly nitrate, which blocks the tube. With the precaution of excluding oxygen, 
the nitride is loose and porous, and can easily be removed from the tube with a rod ; 
but it is not possible to use a tube twice, for the glass is generally softened and 
deformed. 

(g.) Nitride of aluminium has been investigated by Mallet. * He obtained it in 
crystals by heating the metal to whiteness in a carbon crucible. But aluminium 
shows no tendency to unite with nitrogen at a red heat, and cannot be used as an 
absorbent for the gas. 

(h.) GERRESHEint states that he has induced combination between nitrogen and 
mercury ; but the affinity between these elements is of the slightest, for the 
compound is explosive. 

(i.) In addition to these, metallic manganese in a finely divided state has been 
shown to absorb nitrogen at a not very elevated temperature, forming a nitride of the 
formula Mn 5 N 2 4 

(j.) [A mixture of nitrogen with hydrogen, standing over acid, is absorbed at a 
fair rate under the influence of electric sparks. But with an apparatus such as 
that shown in fig. 1, the efficiency is but a fraction (perhaps ^) of that obtainable 
when oxygen is substituted for hydrogen and alkali for acid. — April, 1895.] 

4. Early Experiments on sparking Nitrogen ivith Oxygen in presence of Alkali. 

In our earliest attempts to isolate the suspected gas by the method of Cavendish, 
we used a Bdhmkorff coil of medium size actuated by a battery of five Grove cells. 
The gases were contained in a test-tube A, fig. 1, standing over a large quantity of 
weak alkali B, and the current was conveyed in wires insulated by U-shaped glass 
tubes CC passing through the liquid round the mouth of the test tube. The inner 
platinum ends DD of the wires were sealed into the glass insulating tubes, but 
reliance was not placed upon these sealings. In order to secure tightness in spite 
of cracks, mercury was placed in the bends. This disposition of the electrodes 
complicates the apparatus somewhat and entails the use of a large depth of liquid in 
order to render possible the withdrawal of the tubes, but it has the great advantage 
of dispensing with sealing electrodes of platinum into the principal vessel, which 
might give way and cause the loss of the experiment at the most inconvenient 
moment. "With the given battery and coil a somewhat short spark, or arc, of about 
5 minims, was found to be more favourable than a longer one. When the mixed 
gases were in the right proportion, the rate of absorption was about 30 cub. centims. 

* ' Journ. Chem. Soc.,' 1876, vol. 2, p. 349. 

t ' Annalen der Chemie u. Pharrnacie,' 195, 373. 

X 0. Pkehlingee, 'Monatsh. f. Chemie,' 15, 391. 



198 



LORD RATLEIGH AND PROFESSOR W. RAMSAY ON ARGON, 



per hour, or 30 times as fast as Cavendish could work with the electrical machine 
of his day. 

To take an example, one experiment of this kind started with 50 cub. centims. of air. 
To this, oxygen was gradually added until, oxygen being in excess, there was no 
perceptible contraction during an hour's sparking. The remaining gas was then 
transferred at the pneumatic trough to a small measuring vessel, sealed by mercury, 

Fig. 1. 




in which the volume was found to be 1 "0 cub. centim. On treatment with alkaline 
pyrogallate, the gas slrrank to "32 cub. centim. That this small residue could not be 
nitrogen was argued from the fact that it had withstood the prolonged action of the 
spark, although mixed with oxygen in nearly the most favourable proportion. 

The residue was then transferred to the test-tube with an addition of another 
50 cub. centims. of air, and the whole worked up with oxygen as before. The residue 
was now 2*2 cub. centims., and, after removal of oxygen, "76 cub. centim. 



A NEW CONSTITUENT OF THE ATMOSPHERE. 199 

Although it seemed almost impossible that these residues could be either nitrogen 
or hydrogen, some anxiety was not unnatural, seeing that the final sparking took 
place under somewhat abnormal conditions. The space was very restricted, and the 
temperature (and with it the proportion of aqueous vapour) was unduly high. But 
any doubts that were felt upon this score were removed by comparison experiments 
in which the whole quantity of air operated on was very small. Thus, when a 
mixture of 5 cub. centhns. of air with 7 cub. centims. of oxygen was sparked for one 
hour and a quarter, the residue was *47 cub. centim., and, after removal of oxygen, 
•06 cub. centim. Several repetitions having given similar results, it became clear 
that the final residue did not depend upon anything that might happen when sparks 
passed through a greatly reduced volume, but was in proportion to the amount of air 
operated upon. 

No satisfactory examination of the residue which refused to be oxidised could be 
made without the accumulation of a larger quantity. This, however, was difficult of 
attainment at the time in question. The gas seemed to rebel against the law of 
addition. It was thought that the cause probably lay in the solubility of the gas in 
water, a suspicion since confirmed. At length, however, a sufficiency was collected 
to allow of sparking in a specially constructed tube, when a comparison with the air 
spectrum taken under similar conditions proved that, at any rate, the gas was not 
nitrogen. At first scarcely a trace of the principal nitrogen lines could be seen, but 
after standing over water for an hour or two these lines became apparent. 

[The apparatus shown in fig. 1 has proved to be convenient for the purification of 
small quantities of argon, and for determinations of the amount of argon present in 
various samples of gas, e.g., in the gases expelled from solution in water. To set it 
in action an alternating current is much to be preferred to a battery and break. At 
the Royal Institution the primary of a small Ruhmkorff was fed from the 100-volt 
alternating current supply, controlled by two large incandescent lamps in series with 
the coil. With this arrangement the voltage at the terminals of the secondary, 
available for starting the sparks, was about 2000, and could be raised to 4000 by 
plugging out one of the lamps. With both lamps in use the rate of absorption of 
mixed gases was 80 cub. centims. per hour, and this was about as much as could well 
be carried out in a test-tube. Even with this amount of power it was found better 
to abandon the sealings at D. No inconvenience arises from the open ends, if the 
tubes are wide enough to ensure the liberation of any gas included over the mercury 
when they are sunk below the liquid. 

The power actually expended upon the coil is very small. When the apparatus is 
at work the current taken is only 2 - 4 amperes. As regards the voltage, by far the 
greater part is consumed in the lamps. The efficient voltage at the terminals of the 
primary coil is best found indirectly. Thus, if A be the current in amperes, V the 
total voltage, V x the voltage at the terminals of the coil, V 2 that at the terminals of 
the lamps, the watts used are* 

* Ayeton and Sdmpnee, ' Proc. Roy. Soc.,' vol. 49, p. 427, 1891. 



200 



LORD RAYLEIGH AND PROFESSOR W. RAMSAY ON ARGON, 



In the present case a Cabdew voltmeter gave V = 90^, V 3 = 
formula may be neglected. Thus, 



and V] 3 in the 



A 



W = ^(V + V 2 )(V - V 8 ) = A(V - V £ ) 

= 2" 4 X 2 "5 = 6"0 approximately. 

The work consumed by the coil when the sparks are passing is, thus, less than -3-0 0T> 
a horse-power ; but, in designing an apparatus, it must further be remembered that 
in order to maintain the arc, a pretty high voltage is required at the terminals of the 
secondary when no current is passing in it. — April, 1895.] 



5. Early Experiments on Withdrawal of Nitrogen from Air by means of Red-hot 

Magnesium. 

It having been proved that nitrogen, at a bright red heat, was easily absorbed 
by magnesium, best in the form of turnings, an attempt was successfully made to 
remove that gas from the residue left after eliminating oxygen from air by means of 
red-hot copper. 

Fig. 2. 




The preliminary experiment was made in the following manner : — A combustion 
tube, A, was filled with magnesium turnings, packed tightly by pushing them in with 
a rod. This tube was connected with a second piece of combustion tubing, B, by 
means of thick-walled india-rubber tubing, carefully wired ; B contained copper oxide, 
and, in its turn, was connected with the tube CD, one-half of which contained soda- 
lime, previously ignited to expel moisture, while the other half was filled with 
phosphoric anhydride. E is a measuring vessel, and F is a gas-holder containing 
"atmospheric nitrogen." 



A NEW CONSTITUENT OP THE ATMOSPHERE. 



201 



In beginning an experiment, the tubes were heated with long-flame burners, and 
pumped empty ; a little hydrogen was formed by the action of the moisture on the 
metallic magnesium ; it was oxidised by the copper oxide and absorbed by the 
phosphoric pentoxide. A gauge attached to the Sprengel's pump, connected with 
the apparatus, showed when a vacuum had been reached. A quantity of nitrogen 
was then measured in E, and admitted into contact with the red-hot magnesium. 
Absorption took place, rapidly at first and then slowly, as shown by the gauge on the 
Sprengel's pump. A fresh quantity was then measured and admitted, and these 
operations were repeated until no more could be absorbed. The system of tubes was 
then pumped empty by means of the Sprengel's pump, and the gas was collected. 
The magnesium tube was then detached and replaced by another. The unabsorbed 
gas was returned to the measuring-tube by a device shown in the figure (G) and the 
absorption recommenced. After 1094 cub. centims. of gas had been thus treated, 
there was left about 50 cub. centims. of gas, which resisted rapid absorption. It still 
contained nitrogen, however, judging by the diminution of volume which it 
experienced when allowed to stand in contact with red-hot magnesium. Its density 
was, nevertheless, determined by weighing a small bulb of about 40 cub. centims. 
capacity, first with air, and afterwards with the gas. The data are these : — 



(a.) Weight of bulb and air — that of glass counterpoise 
., ,, alone — that of glass counterpoise . 



air 



grm. 
0-8094 

C7588 

0-0506 



(b.) "Weight of bulb and gas — that of glass counterpoise . . . 0*8108 
,, ,, alone — that of glass counterpoise . . . 07588 



gas 0-0520 

Taking as the weight of a litre of air, 1-29347 grms., the mean of the latest 
results, and of oxygen (= 16) 1-42961 grms.,* the density of the residual gas 

is 14-88. 

* The results on which this and the subsequent calculations are based are as follows (the weights 
are those of 1 litre) : — 



Regxault .... 
vox jollt .... 
Ledcc 


Air. 


Oxygen. 


Nitrogen. 


J 
Hydrogen. 


1-29349 
1-29383 
1-29330 
1-29327 


1-43011 
1-42971 
1-42910 
1-42952 


1-25647 
1-25819 
1-25709 
1-25718 


0-08988 

0-08985 
0-09001 



Regxault's numbers have an approximate correction applied to them by CRAFTS. The mean of these 
MLiCCCXCV. — A. 2 D 



202 



LORD RATLEIGH AND PROFESSOR W. RAMSAY ON ARGON, 



This result was encouraging, although weighted with the unavoidable error attach- 
ing to the weighing of a very small amount. Still the fact remains that the supposed 
nitrogen was heavier than air. It would hardly have been possible to make a mistake 
of 27 milligrams. 

It is right here to place on record the fact that this first experiment was to a great 
extent carried out by Mr. Percy Williams, to whose skill in manipulation and great 
care its success is due, and to whom we desire here to express our thanks. 

Experiments were now begun on a larger scale, the apparatus employed being shown 



in figs. 3 and 4. 



Eiff. 3. 





F a 

Soda-lime 



A and B are large glass gas-holders of about 10 litres capacity. C is an arrange- 
ment by which gas could be introduced at will into the gas-holder A, either by means 
of an india-rubber tube slipped over the open end of the U-tube, or, as shown in the 
figure, from a test-tube. The tube D was half filled with soda-lime (a), half with 
phosphoric anhydride (b). Similarly, the tube E, which was kept at a red heat by 
means of the long-flame burner, was filled half with very porous copper (a), reduced 
from dusty oxide by heating in hydrogen, half with copper oxide in a granular form (6). 
The next tube, F, contained granular soda-lime, while G contained magnesium turn- 
numbers is taken, that of Regxatjlt for nitrogen being omitted, as there is reason to believe that 
his specimen was contaminated with hydrogen. 



Air. 


Oxygen. 


Nitrogen. 


Hydrogen. 


1-29347 


1-42961 


1-25749 


0-08991 



This ratio gives for air the composition by volume — 

Oxygen 20-91 per cent. 

Nitrogen 79-09 „ 

a result verified by experiment. 

It is, of course, to be understood that these densities of nitrogen refer to atmospheric nitrogen, 
that is, to air from which oxygen, water vapour carbon dioxide, and ammonia have been removed. 



A NEW CONSTITUENT OF THE ATMOSPHERE. 



203 



ings, also heated to bright redness by means of a long-flame burner. H contained 
phosphoric anhydride, and I soda-lime. All joints were sealed, excepting those 
connecting the hard-glass tubes E and G to the tubes next them. 

The gas-holder A having been filled with nitrogen, prepared by passing air over red- 
hot copper, and introduced at C, the gas was slowly passed through the system of 
tubes into the gas-holder B, and back again. The magnesium in the tube G having 
then ceased to absorb was quickly removed and replaced by a fresh tube. This tube 
was of course full of air, and before the tube G was heated, the air was carried back 
from B towards A by passing a little nitrogen from right to left. The oxygen in the 
air was removed by the metallic copper, and the nitrogen passed into the gas-holder 
A, to be returned in the opposite direction to B. 



Fig. i. 



To Spnngelf ^ 




In the course of about ten clays most of the nitrogen had been absorbed. The 
magnesium was not always completely exhausted ; usually the nitride presented the 
appearance of a blackish- yellow mass, easily shaken out of the tube. It is needless to 
say that the tube was always somewhat attacked, becoming black with a coating of 
magnesium silicide. The nitride of magnesium, whether blackish or orange, if left 
for a few hours exposed to moist air, was completely converted into white, dusty 
hydroxide, and during exposure it gave off a strong odour of ammonia. If kept in a 
stoppered bottle, however, it was quite stable. 

It was then necessary, in order to continue the absorption, to carry on operations 
on a smaller scale, with precautions to exclude atmospheric air as completely as 
possible. There was at this stage a residue of 1500 cub. centims. 

The apparatus was therefore altered to that shown in fig. 4, so as to make it possible 
to withdraw all the gas out of the gas-holder A. 

The left-hand exit led to the Spkengel's pump ; the compartment (a) of the 
drying-tube B was filled with soda-lime, and (b) with phosphoric anhydride. C is a 

2 D 2 



204 LORD RAYLEIGH AND PROFESSOR W. RAMSAY ON ARGON, 

tube into which the gas could be drawn from the gas-holder A. The stop-cock, as 
shown, allows gas to pass through the horizontal tubes, and does not communicate 
with A ; but a vertical groove allows it to be placed in communication either with the 
gas-holder, or with the apparatus to the right. The compartment (a) of the second 
drying-tube D contained soda-lime, and (b) phosphoric anhydride. The tube D com- 
municated with a hard-glass tube E, heated over a long-flame burner ; it was partly 
filled with metallic copper, and partly with copper oxide. This tube, as well as the 
tube F filled with magnesium turnings, was connected to the drying-tube with india- 
rubber. The gas then entered G, a graduated reservoir, and the arrangement H 
permitted the removal or introduction of gas from or into the apparatus. The gas 
was gradually transferred from the gas-holder to the tube C, and passed backwards 
and forwards over the red-hot magnesium until only about 200 cub. centims. were 
left. It was necessary to change the magnesium tube, which was made of smaller 
size than formerly, several times during the operation. This was done by turning out 
the long-flame burners and pumping off all gas in the horizontal tubes by means of 
the Speengel's pump. This gas was carefully collected. The magnesium tube was 
then exchanged for a fresh one, and after air had been exhausted from the apparatus, 
nitrogen was introduced from the reservoir. Any gas evolved from the magnesium 
(and apparently there was always a trace of hydrogen, either occluded by the magne- 
sium, or produced by the action of aqueous vapour on the metal) was oxidised by the 
copper oxide. Had oxygen been present, it would have been absorbed by the metallic 
copper, but the copper preserved its red appearance without alteration, whereas a little 
copper oxide was reduced during the series of operations. The gas, which had been 
removed by pumping, was reintroduced at H, and the absorption continued. 

The volume of the gas was thus, as has been said, reduced to about 200 cub. 
centims. It would have been advisable to take exact measurements, but, unfor- 
tunately, some of the original nitrogen had been lost through leakage ; and a natural 
anxiety to see if there was any unknown gas led to pushing on operations as quickly 
as possible. 

The density of the gas was next determined. The bulb or globe in which the gas 
was weighed was sealed to a two-way stop-cock, and the weight of distilled and 
air-free water filling it at 17"15° was 162 - 654 grms., corresponding to a capacity of 
162*843 cub. centims. The shrinkage on removing air completely was 0"0212 cub. 
centim. Its weight, when empty, should therefore be increased by the weight of 
that volume of air, which may be taken as "000026 grin. This correction, however, 
is perhaps hardly worth applying in the present case. 

The counterpoise was an exactly similar bulb of equal capacity, and weighing about 
0'2 grin, heavier than the empty globe. The balance was a very sensitive one by 
Oertling, which easily registered one-tenth of a milligrm. By the process of 
swinging, one-hundredth of a milligrm. could be determined with fair accuracy, 

In weighing the empty globe, 0"2 grm. was placed on the same pan as that which 



A NEW CONSTITUENT OF THE ATMOSPHERE. 205 

hung from the end of the beam to which it was suspended, and the final weight was 
adjusted by means of a rider, or by small weights on the other pan. This process 
practically leads to weighing by substitution of gas for weights. The bulb was 
always handled with gloves, to avoid moisture or grease from the fingers. 

Three experiments, of which it is unnecessary to give details, were made to test 
the degree of accuracy with which a gas could be weighed, the gas being dried air, 
freed from carbon dioxide. The mean result gave for the weight of one litre of air 
at 0° and 760 millims. pressure, T2935 grm. Regnault found 1 "29340, a correction 
having been applied by Crafts to allow for the estimated alteration of volume caused 
by the contraction of his vacuous bulb. The mean result of determinations by several 
observers is 1 "29347 ; while one of us found 1 "29327. 

The globe was then filled with the carefully dried gas. 

Temperature, 18"80°. Pressure, 759"3 millims. 

Weight of 162-843 cub. centims. of gas 0-21897 grm. 

Weight -of 1 litre gas at 0° and 760 millims 1-4386 „ 

Density, that of air compared with 0, = 16, being 14-476 16 - 100 grms. 

It is evident from these numbers that the dense constituent of the air was being- 
concentrated. As a check, the bulb was pumped empty and again weighed ; its 
weight was 0'21903 grm. This makes the density 16*105. 

It appeared advisable to continue to absorb nitrogen from this gas. The first tube 
of magnesium removed a considerable quantity of gas ; the nitride was converted 
into ammonium chloride, and the sample contained 66*30 per cent, of chlorine, 
showing, as has before been remarked, that if any of the heavier constituent of the 
atmosphere had been absorbed, it formed no basic compound with hydi-ogen. The 
second tube of magnesium was hardly attacked ; most of the magnesium had melted, 
and formed a layer at the lower part of the tube. That which was still left in the 
body of the tube was black on the surface, but had evidently not been much attacked. 
The ammonium chloride which it yielded weighed only - 0035 gi-m. 

The density of the remaining gas was then determined. But as its volume was 
only a little over 100 cub. centims., the bulb, the capacity of which was 162 cub. 
centims., had to be filled at reduced pressure. This was easily done by replacing the 
pear-shaped reservoir of the mercury gas-holder by a straight tube, and noting the 
level of the mercury in the gas-holder and in the tube which served as a mercury 
reservoir against a graduated mirror-scale by help of a cathetomer at the moment of 
closing the stop-cock of the density bulb. 

The details of the experiment are these : — 

Temperature, 19-12° C. Barometric pressure, 749-8 millims. (corr.). 
Difference read on gas-holder and tube, 225'25 millims. (corr.). 
Actual pressure, 5 24 "5 5 millims. 



206 LORD RAYLEIGH AND PROFESSOR W. RAMSAY ON ARGON, 

Weight of 162*843 cub. centims. of gas . . . . . 0*17913 grin. 
Weight of 1 litre at 0° and 760 millims. pressure . . 17054 ,, 
Density 19-086 grms. 

This gas is accordingly at least 19 times as heavy as hydrogen. 

A portion of the gas was then mixed with oxygen, and submitted to a rapid 
discharge of sparks for four hours in presence of caustic potash. It contracted, and 
on absorbing the excess of oxygen with pyrogallate of potassium the contraction 
amounted to 15 "4 per cent, of the original volume. The question then arises, if the 
gas contain 15'4 per cent, of nitrogen, of density 14*014, and 84*6 per cent, of other 
gas, and if the density of the mixture were 19 "08 6, what would be the density of the 
other gas ? Calculation leads to the number 20 "0. 

A vacuum-tube was filled with a specimen of the gas of density 19 '08 6, and it 
could not be doubted that it contained nitrogen, the bands of which were distinctly 
visible. It was probable, therefore, that the true density of the pure gas lay not far 
from 20 times that of hydrogen. At the same time many lines were seen which 
could not be recognized as belonging to the spectrum of any known substance. 

Such Avere the preliminary experiments made with the aid of magnesium to 
separate from atmospheric nitrogen its dense constituent. The methods adopted in 
preparing large quantities will be subsequently described. 

6. Proof of the Presence of Argon in Air, by means of Atmolysis. 

It has already (§ 2) been suggested that if " atmospheric nitrogen " contains two 
gases of different densities, it should be possible to obtain direct evidence of the fact 
by the method of atmolysis. The present section contains an account of carefully 
conducted experiments directed to this end. 

The atmolyser was prepared (after Graham) by combining a number of " church- 
warden " tobacco pipes. At first twelve pipes were used in three groups, each group 
including four pipes connected in series. The three groups were then connected in 
parallel, and placed in a large glass tube closed in such a way that a partial vacuum 
could be maintained in the space outside the pipes by a water-pump. One end of 
the combination of pipes was open to the atmosphere, or rather was connected witb 
the interior of an open bottle containing sticks of caustic alkali, the object being 
mainly to dry the air. The other end of the combination was connected to a bottle 
aspirator, initially full of water, and so arranged as to draw about two per cent, of 
the air which entered the other end of the pipes. The gas collected was thus a very 
small proportion of that which leaked through the pores of the pipes, and should be 
relatively rich in the heavier constituents of the atmosphere. The flow of water 
from the aspirator could not be maintained very constant, but the rate of two per 
cent, was never much exceeded. The necessary four litres took about sixteen hours 
to collect. 



A NEW CONSTITUENT OE THE ATMOSPHERE. 207 

The air thus obtained was treated exactly as ordinary air had been treated in 
determinations of the density of atmospheric nitrogen. Oxygen was removed by 
red-hot copper followed by cupric oxide, ammonia by sulphuric acid, carbonic anhy- 
dride and moisture by potash and phosphoric anhydride. 

The following are the results : — 

Globe empty July 10, 14 2-81789 

Globe full September 15 (twelve pipes) . . - 50286 

Weight of gas 2-31503 

Ordinary atmospheric nitrogen 2"31016 

Difference ".'"/.'..'+ -00487 

Globe empty September 17 2-81345 

Globe full September 18 (twelve pipes) . . -50191 

Weight of gas ........... 2 - 31154 

Ordinary atmospheric nitrogen 2 - 31016 

Difference ......... + "00138 

Globe empty September 21 2-82320 

Globe full September 20 (twelve pipes) . ; "51031 

Weight of gas 2"31289 

Ordinary atmospheric nitrogen 2 - 31016 

Difference . + "00273 

Globe empty September 21, October 30 . . 2"82306 
Globe full September 22 (twelve pipes) . . "51140 

Weight of gas 2-31166 

Ordinary atmospheric nitrogen . . . . , 2 '3101 6 

Difference + "00150 

The mean excess of the four determinations is "00262 gram., or if we omit the first, 
which depended upon a vacuum weighing of two months old, "00187 gram. 

The gas from prepared air was thus in every case denser than from unprepared air, 
and to an extent much beyond the possible errors of experiment. The excess was, 
however, less than had been expected, and it was thought that the arrangement of 
the pipes could be improved. The final delivery of gas from each of the groups in 
parallel being so small in comparison with the whole streams concerned, it seemed 
possible that each group was not contributing its proper share, and even that there 
might be a flow in the wrong direction at the delivery end of one or two of them. To 



208 LORD RAYLEIGH AND PROFESSOR W. RAMSAY ON ARGON, 

meet this objection, the arrangement in parallel had to be abandoned, and for the 
remaining experiments eight pipes were connected in simple series. The porous 
surface in operation was thus reduced, but this was partly compensated for by an 
improved vacuum. Two experiments were made under the new conditions : — 

Globe empty, October 30, November 5 . . 2-82313 
Globe full, November 3 (eight pipes) . . . '50930 

Weight of gas 2-31383 

Ordinary atmospheric nitrogen 2 - 31016 

Difference + -00367 

Globe empty, November 5, 8 2*82355 

Globe full, November G (eight pipes) . . . "51011 

Weight of gas 2-31344 

Ordinary atmospheric nitrogen 2 -31016 

Difference + -00328 

The excess being larger than before is doubtless due to the greater efficiency of 
the atmolysing apparatus. It should be mentioned that the above recorded experi- 
ments include all that have been tried, and the conclusion seems inevitable that 
" atmospheric -nitrogen " is a mixture and not a simple body. 

It was hoped that the concentration of the heavier constituent would be sufficient 
to facilitate its preparation in a pure state by the use of prepared air in substitution 
for ordinary air in the oxygen apparatus. The advance of 3 J mg. on the 11 mg., 
by which atmospheric nitrogen is heavier than chemical nitrogen, is indeed not to be 
despised, and the use of prepared air would be convenient if the diffusion apparatus 
could be set up on a large scale and be made thoroughly self-acting. 



7. Negative Experiments to Prove that Argon is not derived from Nitrogen or 

from Cliemical Sources. 

Although the evidence of the existence of argon in the atmosphere, derived from 
the comparison of densities of atmospheric and chemical nitrogen and from the 
diffusion experiments (§ 6), appeared overwhelming, we have thought it undesirable 
to shrink from any labour that would tend to complete the verification. With this 
object in view, an experiment was undertaken and carried to a conclusion on 
November 13, in which 3 litres of chemical nitrogen, prepared from ammonium 
nitrite, were treated with oxygen in precisely the manner in which atmospheric 
nitrogen had been found to yield a residue of argon. In the course of operations an 



A NEW CONSTITUENT OP THE ATMOSPHERE. 209 

accident occurred, by which no gas could have been lost, but of such a nature that 
from 100 to 200 cub. centims. of air must have entered the working vessel. The gas 
remaining at the close of the large scale operations was worked up as usual with 
battery and coil until the spectrum showed only slight traces of the nitrogen lines. 
When cold, the residue measured 4 cub. centims. This was transferred, and after 
treatment with alkaline pyrogallate to remove oxygen, measured 3 '3 cub. centims. 
If atmospheric nitrogen had been employed, the final residue should have been about 
30 cub. centims. Of the 3 "3 cub. centims. actually left, a part is accounted for by 
the accident alluded to, and the result of the experiment is to show that argon is not 
formed by sparking a mixture of oxygen and chemical nitrogen. 

In a second experiment of the same kind 5660 cub. centims. of nitrogen from 
ammonium nitrite were treated with oxygen in the large apparatus (fig. 7, § 8). The 
final residue was 3 '5 cub. centims. ; and as evidenced by the spectrum, it consisted 
mainly of argon. 

The source of the residual argon is to be found in the water used for the 
manipulation of the large quantities of gas (6 litres of nitrogen and 11 litres of 
oxygen) employed. Unfortunately the gases had been collected by allowing them to 
bubble up into aspirators charged with ordinary water, and they were displaced by 
ordinary watei\ In order to obtain information with respect to the contamination 
that may be acquired in this way, a parallel experiment was tried with carbonic 
anhydride. Eleven litres of the gas, prepared from marble and hydrochloric acid 
with ordinary precautions for the exclusion of air, were collected exactly as oxygen 
was commonly collected. It was then transferred by displacement with water to a 
gas pipette charged with a solution containing 100 grms. of caustic soda. The 
residue which refused absorption measured as much as 110 cub. centims. In another 
experiment where the water employed had been partially de-aerated, the residue left 
amounted to 71 cub. centims., of which 26 cub. centims. were oxygen. The 
quantities of dissolved gases thus extracted from water during the collection of 
oxygen and nitrogen suffice to explain the residual argon of the negative experiments. 

It may perhaps be objected that the impurity was contained in the carbonic 
anhydride itself as it issued from the generating vessel, and was not derived from the 
water in the gas-holder ; and indeed there seems to be a general impression that it is 
difficult to obtain carbonic anhydride in a state of purity. To test this question, 
18 litres of the gas, made in the same generator and from the same materials, were 
passed directly into the absorption pipette. Under these conditions, the residue was 
only 6|- cub. centims., corresponding to 4 cub. centims. from- 11 litres. The quantity 
of gas employed was determined by decomposing the resulting sodium carbonate with 
hydrochloric acid, allowance being made for a little carbonic anhydride contained in 
the soda as taken from the stock bottle. It will be seen that there is no difficulty 
in reducing the impurity to -g-^ooth, even when india-rubber connections are freely 
used, and no extraordinary precautions are taken. The large amount of impurity 

MDCCCXCV. — A. 2 E 



210 LORD RAYLEIGK AND PROFESSOR W. RAMSAY 0^ ARGON, 

found in the gas when collected over water must therefore have been extracted from 
the water. 

A similar set of experiments was carried out with magnesium. The nitrogen, of 
which three litres were used, was prepared by the action of bleaching-powder on 
ammonium chloride. It was circulated in the usual apparatus over red-hot magnesium, 
until its volume had been reduced to about 100 cub. centims. An equal volume of 
hydrogen was then added, owing to the impossibility of circulating a vacuum. The 
circulation then proceeded until all absorption had apparently stopped. The remaining 
gas was then passed over red-hot copper oxide into the Sprengel's pump, and 
collected. As it appeared still to contain hydrogen, which had escaped oxidation, 
owing to its great rarefaction, it was passed over copper oxide for a second and a 
third time. As there was still a residue, measuring 12*5 cub. centims., the gas was 
left in contact with red-hot magnesium for several hours, and then pumped out ; its 
volume was then 4 - 5 cub. centims. Absorption was, however, still proceeding, when 
the experiment terminated, for at a low pressure, the rate is exceedingly slow. This 
gas, after being sparked with oxygen contracted to 3 - cub. centims., and on 
examination was seen to consist mainly of argon. The amount of residue obtainable 
from three litres of atmospheric nitrogen should have amounted to a large multiple 
of this quantity. 

In another experiment, 1 5 litres of nitrogen prepared from a mixture of ammonium 
chloride and sodium nitrite by warming in a flask (some nitrogen having first been 
drawn off by a vacuum-pump, in order to expel all air from the flask and from the 
contained liquid) were collected over water in a large gas-holder. The nitrogen was 
not bubbled through the water, but was admitted from above, while the water escaped 
below. This nitrogen was absorbed by red-hot magnesium, contained in tubes heated 
in a combustion-furnace. The unabsorbed gas was circulated over red-hot magnesium 
in a special small apparatus, by which its volume was reduced to 15 cub. centims. 
As it was impracticable further to reduce the volume by means of magnesium, the 
residual 15 cub. centims. were transferred to a tube, mixed with oxygen, and submitted 
to sparking over caustic soda. The residue after absorption of oxygen, which 
undoubtedly consisted of pure argon, amounted to 3"5 cub. centims. This is one-fortieth 
of the quantity which would have been obtained from atmospheric nitrogen, and its 
presence can be accounted for, we venture to think, first from the water in the 
gas-holder, which had not been freed from dissolved gas by boiling in vacuo (it has 
already been shown that a considerable gain may ensue from this source), and second, 
from leakage of air which accidentally took place, owing to the breaking of a tube. 
The leakage may have amounted to 200 cub. centims., but it could not be accurately 
ascertained. Quantitative negative experiments of this nature are exceedingly 
difficult, and require a long time to carry them to a successful conclusion. 



A NEW CONSTITUENT OP THE ATMOSPHERE. 211 

8. Separation of Argon on a Large Scale. 

To separate nitrogen from " atmospheric nitrogen " on a large scale, by help of 
magnesium, several devices were tried. It is not necessary to describe them all in 
detail. Suffice it to say that an attempt was made to cause a store of " atmospheric 
nitrogen " to circulate by means of a fan, driven by a water -motor. The difficulty 
encountered here was leakage at the bearing of the fan, and the introduced air 
produced a cake which blocked the tube on coming into contact with the magnesium. 
It might have been possible to remove oxygen by metallic copper ; but instead of 
thus complicating the apparatus, a watei'-injector was made use of to induce circula- 
tion. Here also it is unnecessary to enter into details. For, though the plan worked 
well, and although about 120 litres of "atmospheric nitrogen" were absorbed, the 
yield of argon was not large, about 600 cub. centims. having been collected. This 
loss was subsequently discovered to be due partially, at least, to the relatively high 
solubility of argon in water. In order to propel the gas over magnesium, through a 
long combustion-tube packed with turnings, a considerable water-pressure, involving 
a large flow of water, was necessary. The gas was brought into intimate contact 
with this water, and presuming that several thousand litres of water ran through the 
injector, it is obvious that a not inconsiderable amount of argon must have been 
dissolved. Its proportion was increasing at each circulation, and consequently its 
partial pressure also increased. Hence, towards the end of the operation, at least, 
there is every reason to believe that a serious loss had occurred. 

It was next attempted to pass " atmospheric nitrogen " from a gas-holder first 
through a combustion tube of the usual length packed with metallic copper reduced 
from the oxide; then through a small U-tube containing a little water, which was 
intended as an index of the rate of flow ; the gas was then dried by passage through 
tubes filled with soda-lime and phosphoric anhydride ; and it next passed through a 
long iron tube (gas-pipe) packed with magnesium turnings, and heated to bright 
redness in a second combustion-furnace. 

After the iron tube followed a second small U -tube containing water, intended to 
indicate the rate at which the argon escaped into a small gas-holder placed to receive 
it. The nitrogen was absorbed rapidly, and argon entered the small gas-holder. But 
there was reason to suspect that the iron tube is permeable by argon at a red heat. 
The first tube-full allowed very little argon to pass. After it had been removed and 
replaced by a second, the same thing was noticed. The first tube was difficult to 
clean ; the nitride of magnesium forms a cake on the interior of the tube, and it was 
very difficult to remove it ; moreover this rendered the filling of the tube very 
troublesome, inasmuch as its interior was so rough that the magnesium turnings could 
only with difficulty be forced down. However, the permeability to argon, if such be 
the case, appeared to have decreased. The iron tube was coated internally with a 
skin of magnesium nitride, which appeared to diminish its permeability to argon. 

9. v 9 



212 



LORD RAYLEIGH AND PROFESSOR W. RAMSAY ON ARGON, 



After all the magnesium in the tube had been converted into nitride (and this was 
easily known, because a bright glow proceeded gradually from one end of the tube to 
the other) the argon remaining in the iron tube was "washed " out by a current of 
nitrogen ; so that after a number of operations, the small gas-holder contained a 
mixture of argon with a considerable quantity of nitrogen. 

On the whole, the use of iron tubes is not to be recommended, owing to the diffi- 
culty in cleaning them, and the possible loss through their permeability to argon. 
There is no such risk of loss with glass tubes, but each operation requires a new tube, 
and the cost of the glass is considerable if much nitrogen is to be absorbed. Tubes 
of porcelain were tried ; but the glaze in the interior is destroyed by the action of the 
red-hot magnesium, and the tubes crack on cooling. 

By these pi'ocesses 157 litres of "atmospheric nitrogen" were reduced in volume to 
about 2'5 litres in all of a mixture of nitrogen and argon. This mixture was after- 
wards circulated over red-hot magnesium, in order to remove the last portion of 
nitrogen. 



Fig. 5. 



T<t water-pu-mp 



To Spre.nqp.Vs 
pump 




As the apparatus employed for this purpose proved very convenient, a full descrip- 
tion of its construction is here given. A diagram is shown in fig. 5, which sufficiently 
explains the arrangement of the apparatus. A is the circulator. It consists of a sort 
of Sprengel's pump (a) to which a supply of mercury is admitted from a small 



A NEW CONSTITUENT OF THE ATMOSPHERE. 213 

reservoir (6). This mercury is delivered into a gas-separator (c), and the mercury 
overflows into the reservoir (d). When its level rises, so that it blocks the tube (/), 
it ascends in pellets or pistons into (e), a reservoir which is connected through (g) 
with a water-pump. The mercury falls into (b), and again passes down the Sprengel 
tube (a). No attention is, therefore, required, for the apparatus works quite auto- 
matically. This form of apparatus was employed several years ago by Dr. Collie. 

The gas is drawn from the gas-holder B, and passes through a tube C, which is 
heated to redness by a long-flame burner, and which contains in one half metallic 
copper, and in the other half copper oxide. This precaution is taken in order to remove 
any oxygen which may possibly be present, and also any hydrogen or hydrocarbon. 
In practice, it was never found that the copper became oxidised, or the oxide reduced. 
It is, however, useful to guard against any possible contamination. The gas next 
traversed a drying-tube D, the anterior portion containing ignited soda-lime, and the 
posterior portion phosphoric anhydride. From this it passed a reservoir, D', from 
which it could be transferred, when all absorption had ceased, into the small gas- 
holder. It then passed through E, a piece of combustion-tube, drawn out at both 
ends, filled with magnesium turnings, and heated by a long-flame burner to redness. 
Passing through a small bulb, provided with electrodes, it again entered the fall 
tube. 

After the magnesium tube E had done its work, the stop-cocks were all closed, and 
the gas was turned down, so that the burners might cool. The mixture of argon and 
nitrogen remaining in the system of tubes was pumped out by a Sprengel's pump 
through F, collected in a large test-tube, and reintroduced into the gas-holder B 
through the side-tube G, which requires no description. The magnesium tube was 
then replaced by a fresh one ; the system of tubes was exhausted of air ; argon and 
nitrogen were admitted from the gas-holder B ; the copper-oxide tube and the 
magnesium tube were again heated ; and the operation was repeated until absorption 
ceased. It was easy to decide when this point had been reached, by making use of 
the graduated cylinder H, from which water entered the gas-holder B. It was found 
advisable to keep all the water employed in these operations, for it had become 
saturated with argon. If gas was withdrawn from the gas-holder, its place was taken 
by this saturated water. 

The absorption of nitrogen proceeds very slowly towards the end of the operation, 
and the diminution in volume of the gas is not greater than 4 or 5 cub. centims. per 
hour. It is, therefore, somewhat difficult to judge of the end-point, as will be seen 
when experiments on the density of this gas are described. The magnesium tube, 
towards the end of the operations, was made so hot that the metal was melted in the 
lower part of the tube, and sublimed in the upper part. The argon and residual 
nitrogen had, therefore, been thoroughly mixed with gaseous magnesium during its 
passage through the tube E. 

To avoid possible contamination with air in the Sprengel's pump, the last portion 



214 LORD RAYLEIGH AND PROFESSOR W. RAMSAY ON ARGON, 

of gas collected from the system of tubes was not re-admitted to the gas-holder B, but 
was separately stored. 

The crude argon was collected in two operations. First, the quantity made by 
absorption by magnesium in glass tubes with the water-pump circulator was purified. 
Later, after a second supply had been prepared by absorption in iron tubes, the mixture 
of argon and nitrogen was united with the first quantity and circulated by means of the 
mercury circulator, in the gas-holder B. Attention will be drawn to the particular 
sample of gas employed in describing further experiments made with the argon. 

By means of magnesium, about 7 litres of nitrogen can be absorbed in an hour. 
The changing of the tubes of magnesium, however, takes some time ; consequently, 
the largest amount absorbed in one day was nearly 30 litres. 

At a later date a quantitative experiment was carried out on a large scale, the 
amount of argon from 100 litres of "atmospheric" nitrogen, measured at 20°, having 
been absorbed by magnesium, and the resulting argon measured at 12°. During the 
process of absorbing nitrogen in the combustion-furnace, however, one tube cracked, 
and it is estimated that about 4 litres of nitrogen escaped before the crack was 
noticed. With this deduction, and assuming that the nitrogen had been measured at 
12°, 93 "4 litres of atmospheric nitrogen were taken. The magnesium required for 
absorption weighed 409 grms. The amount required by theory should have been 
285 grms. ; but it must be remembered that in many cases the magnesium was by no 
means wholly converted into nitride. The first operation yielded about 3 litres of a 
mixture of nitrogen and argon, which was purified in the circulating apparatus. The 
total residue, after absorption of the nitrogen, amounted to 921 cub. centims. The 
yield is therefore 0'986 per cent. 

At first no doubt the nitrogen gains a little argon from the water over which it 
stands. But, later, when the argon forms the greater portion of the gaseous mixture, 
its solubility in water must materially decrease its volume. It is difficult to estimate 
the loss from this cause. The gas-holder, from which the final circulation took place, 
held three litres of water. Taking the solubility of argon as 4 per cent., this would 
mean a loss of about 120 cub. centims. If this is not an over-estimate, the yield of 
argon would be increased to 1040 cub. centims., or I'll per cent. The truth probably 
lies between these two estimates. 

It may be concluded, with probability, that the argon forms approximately 1 per 
cent, of the " atmospheric " nitrogen. 

The principal objection to the oxygen method of isolating argon, as hitherto 
described, is the extreme slowness of the operation. An absorption of 30 cub. 
centims. of mixed gas means the removal of but 12 cub. centims. of nitrogen. At 
this rate 8 hours are required for the isolation of 1 cub. centim. of argon, supposed 
to be present in the proportion of 1 per cent. 

In extending the scale of operations we had the great advantage of the advice of 



A NEW" CONSTITUENT OF THE ATMOSPHERE. 215 

Mr. Crookes, who a short time ago called attention to the flame rising from platinum 
terminals, which convey a high tension alternating electric discharge, and pointed 
out its dependence upon combustion of the nitrogen and oxygen of the air.* 
Mr. Crookes was kind enough to arrange an impromptu demonstration at his own 
house with a small alternating current plant, in which it appeared that the absorp- 
tion of mixed gas was at the rate of 500 cub. centims. per hour, or nearly 20 times 
as fast as with the battery. The arrangement is similar to that first described by 
SpoTTiswooDE.f The primary of a Ruhmkorff coil is connected directly with the 
alternator, no break or condenser being required ; so that, in fact, the coil acts 
simply as a high potential transformer. When the arc is established the platinum 
terminals may be separated much beyond the initial striking distance. - 

The plant with which the large scale operations have been made consists of a 
De Meritens alternator, kindly lent by Professor J. J. Thomson, and a gas engine. 
As transformer, one of Swinburne's hedgehog pattern has been employed with 
success, but the ratio of transformation (24 : 1) is scarcely sufficient. A higher 
potential, although, perhaps, not more efficient, is more convenient. The striking 
distance is greater, and the arc is not so liable to go out. Accordingly moist of the 
work to be described has been performed with transformers of the Ruhmkoree type. 

The apparatus has been varied greatly, and it cannot be regarded as having even 
yet assumed a final form. But it will give a sufficient idea of the method if we 
describe an experiment in which a tolerably good account was kept of the air and 
oxygen employed. The working' vessel was a glass flask, A (fig. 6), of about 1500 cub. 
centims. capacity, and stood, neck downwards, over a large jar of alkali, B. As in 
the small scale experiments, the leading-in wires were insulated by glass tubes, DD, 
suitably bent and carried through the liquid up the neck. For the greater part of 
the length iron wires were employed, but the internal extremities, EE, were of 
platinum, doubled upon itself at the terminals from which the discharge escaped. 
The glass protecting tubes must be carried up for some distance above the internal 
level of the liquid, but it is desirable that the arc itself should not be much raised 
above that level. A general idea of the disposition of the electrodes will be obtained 
from fig. 6. To ensure gas tightness the bends were occupied by mercury. A tube, 
C, for the supply or withdrawal of gas was carried in the same way through the 
neck. 

The Btjhiikorff employed in this operation was one of medium size. When the 
mixture was rightly proportioned and the arc of full length, the rate of absorption 
was about 700 cub. centims. per hour. A good deal of time is lost in starting, for, 
especially when there is soda on the platinums, the arc is liable to go out if lengthened 
prematurely. After seven days the total quantity of air let in amounted to 7925 cub. 
centims,, and of oxygen (prepared from chlorate of potash) 9137 cub. centims. On 

* '■ Chemical News,' vol. 65, p. 301, 1892. 

t " A Mode of Exciting an Inchiction-coil." ' Phil. Mag.,' vol. 8, p. 390, 1879. 



216 



LORD RAYLEIGH AND PROFESSOR W. RAMSAY ON ARGON, 



the eighth and ninth days oxygen alone was added, of which ahont 500 cub. centims. 
was consumed, while there remained about 700 cub. centims in the flask. Hence the 
proportion in which the air and oxygen combined was as 70:96. On the eighth day 
there was about three hours' work, and the absorption slackened off to about one 
quarter of the previous rate. On the ninth day (September 8) the rate fell off still 




more, and after three hours' work became very slow. The progress towards removal 
of nitrogen was examined from time to time with the spectroscope, the points being 
approximated and connected with a small Leyden jar. At this stage the yellow 
- nitrogen line w T as faint, but plainly visible. After about four hours' more work, the 
yellow line had disappeared, and for two hours there had been no visible contraction. 
It will be seen that the removal of the last part of the nitrogen was very slow, mainly 
on account of the large excess of oxygen present. 



A NEW CONSTITUENT OF THE ATMOSPHERE. 217 

The final treatment of the residual 700 cub. centitns. of gas was on the model of 
the small scale operations already described (§ 4). By means of a pipette the gas was 
gradually transferred to a large test-tube standing over alkali. Under the influence 
of sparks (from battery and coil) passing all the while, the superfluous oxygen was 
consumed with hydrogen fed in slowly from a voltameter. If the nitrogen had been 
completely removed, and if there were no unknown ingredient in the atmosphere, the 
volume under this treatment should have diminished without limit. But the con- 
traction stopped at a volume of 65 cub. centims., and the volume was taken back- 
wards and forwards through this as a minimum by alternate treatment with oxygen 
and hydrogen added in small quantities, with prolonged intervals of sparking. 
Whether the oxygen or the hydrogen were in excess could be determined at any 
moment by a glance at the spectrum. At the minimum volume the gas was certainly 
not hvdrogen or oxygen. Was it nitrogen % On this point the testimony of the 
spectroscope was equally decisive. No trace of the yellow nitrogen line could be seen 
even with a wide slit and under the most favourable conditions. 

When the gas stood for some days over water the nitrogen line again asserted 
itself, and many hours of sparking with a little oxygen were required again to get rid of 
it. As it was important to know what proportions of nitrogen could be made visible 
in this way, a little air was added to gas that had been sparked for some time subse- 
quently to the disappearance of nitrogen in its spectrum. It was found that about 
1^ per cent, was clearly, and about 3 per cent, was conspicuously, visible. About the 
same numbers apply to the visibility of nitrogen in oxygen when sparked under these 
conditions, that is, at atmospheric pressure, and with a jar in connection with the 
secondary terminals. 

When we attempt to increase the rate of absorption by the use of a more powerful 
electric arc, further experimental difficulties present themselves. In the arrangement 
already described, giving an absorption of 700 cub. centims. per hour, the upper part 
of the flask becomes very hot. With a more powerful arc the heat rises to such a 
point that the flask is filled with steam and the operation comes to a standstill. 

It is necessary to keep the vessel cool by either the external or internal application 
of liquid to the upper surface upon which the hot gases from the arc impinge. One 
way of effecting this is to cause a small fountain of alkali to impinge on the top of 
the flask, so as to wash the whole of the upper surface. This plan is very effective, 
but it is open to the objection that a break-down would be disastrous, and it would 
involve special arrangements to avoid losing the argon by solution in the large 
quantity of alkali required. It is simpler in many respects to keep the vessel cool by 
immersing it in a large body of water, and the inverted flask arrangement (fig. 6) has 
been applied in this manner. But, on the whole, it appears to be preferable to limit 
the application of the cooling water to the upper part of the external surface, building 
up for this purpose a suitable wall of sheet lead cemented round the glass. The most 

MDCCCXCV. — A. 2 F 



218 



LORD RATLEIGH AND PROFESSOR W. RAMSAY ON ARGON, 



convenient apparatus for large-scale operations that has hitherto been tried is shown 
in the accompanying figure (fig. 7). 

The vessel A is a large globe of about 6 litres capacity, intended for demonstrating 
the combustion of phosphorus in oxygen gas, and stands in an inclined position. It 
is about half filled with a solution of caustic soda. The neck is fitted with a rubber 
stopper, B, provided with four perforations. Two of these are fitted with tubes, 
C, D, suitable for the supply or withdrawal of gas or liquid. The other two allow 
the passage of the stout glass tubes, E, F, which contain the electrodes. For greater 
security against leakage, the interior of these tubes is charged with water, held in 
place by small corks, and the outer ends are cemented up. The electrodes are formed 



Fig. 7. 




Sea 1 e 5 



of stout iron wires terminated by thick platinums, G, H, triply folded together, and 
welded at the ends. The lead walls required to enclose the cooling water are 
partially shown at I. For greater security the india-rubber cork is also drowned in 
water, held in place with the aid of sheet-lead. The lower part of the globe is 
occupied by about 3 litres of a 5 per cent, solution of caustic soda, the solution rising 
to within about half-an-inch of the platinum terminals. With this apparatus an 
absorption of 3 litres of mixed gas per hour can be attained, — about 3000 times the 
rate at which Cavendish could work. 

When it is desired to stop operations, the feed of air (or of chemical nitrogen in 
blank experiments) is cut off, oxygen alone being supplied as long as any visible 
absorption occurs. Thus at the close the gas space is occupied by argon and oxygen 
with such nitrogen as cannot readily be taken up in a condition of so great dilution. 



A NEW CONSTITUENT OF THE ATMOSPHERE. 219 

The oxygen, being too much for convenient treatment with hydrogen, was usually 
absorbed with copper and ammonia, and the residual gas was then worked over again 
as already described in an apparatus constructed upon a smaller scale. 

It is worthy of notice that with the removal of the nitrogen, the arc-discbarge from 
the dynamo changes greatly in appearance, bridging over more directly and in a nar- 
rower band from one platinum to the other, and assuming a beautiful sky-blue colour, 
instead of the greenish hue apparent so long as oxidation of nitrogen is in progress. 

In all the large-scale experiments, an attempt was made to keep a reckoning of the 
air and oxygen employed, in the hope of obtaining data as to the proportional 
volume of argon in air, but various accidents too often interfered. In one successful 
experiment (January, 1895), specially undertaken for the sake of measurement, the 
total air employed was 9250 cub. centims., and the oxygen consumed, manipulated 
with the aid of partially de-aerated water, amounted to 10,820 cub. centims. The 
oxygen contained in the air would be 1942 cub. centims. ; so that the quantities of 
"atmospheric nitrogen" and of total oxygen which enter into combination would be 
7308 cub. centims., and 12,762 cub. centims. respectively. This corresponds to 
N + 1"750 — the oxygen being decidedly in excess of the proportion required to form 
nitrous acid — 2HNCX, or H 2 + N a + 30. The argon ultimately found on absorption 
of the excess of oxygen was 75 '0 cub. centims., reduced to conditions similar to 
those under which the air was measured, or a little more than 1 per cent, of the 
" atmospheric nitrogen " used. It is probable, however, that some of the argon was 
lost by solution during the protracted operations required in order to get quit of the 
last traces of nitrogen. 

[In recent operations at the Royal Institution, where a public supply of alternating- 
current at 100 volts is available, the scale of the apparatus has been still further 
increased. 

The capacity of the working vessel is 20 litres, of which about one half is 
occupied by a strong solution of caustic soda. The platinum terminals are very 
massive, and the flame rising from them is prevented from impinging directly upon 
the glass by a plate of platinum held over it and supported by a wire which passes 
through the rubber cork. In the electrical arrangements we have had the advantage 
of Mr. Swinburne's advice. The transformers are two of the " hedgehog " pattern, 
the thick wires being connected in parallel and the thin wires in series. In order to 
control the current taken when the arc is short or the platinums actually in contact, 
a choking-coil, provided with a movable core of fine iron wires, is inserted in the 
thick wire circuit.- In normal working the current taken from the mains is about 
22 amperes, so that some 2 J? h. p. is consumed. At the same time the actual 
voltage at the platinum terminals is 1500. When the discharge ceases, the voltage 
at the platinum rises to 3000,* which is the force actually available for re-starting 
the discharge if momentarily stopped. 

* A still higher voltage on open circuit would be preferable. 

2 F 2 



220 LORD RATLEIGH AND PROFESSOR W. RAMSAY ON ARGON, 

With this discharge, the rate of absorption of mixed gases is about 7 litres per hour. 
When the argon has accumulated to a considerable extent, the rate falls off, and after 
several days' work, about 6 litres per hour becomes the maximum. In commencing 
operations it is advisable to introduce, first, the oxygen necessary to combine with 
the already included air, after which the feed of mixed gases should consist of about 
1 1 parts of oxygen to 9 parts of air. The mixed gases may be contained in a large 
gas-holder, and then, the feed being automatic, very little attention is required. 
When it is desired to determine the rate of absorption, auxiliary gas-holders of glass, 
graduated into litres, are called into play. If the rate is unsatisfactory, a determina- 
tion may be made of the proportion of oxygen in the working vessel, and the 
necessary gas, air, or oxygen, as the case may be, introduced directly. 

In re-starting the arc after a period of intermission, it is desirable to cut off the 
connection with the principal gas-holder. The gas (about two litres in amount) 
ejected from the working vessel by the expansion is then retained in the auxiliary 
holder, and no argon finds its way further back. The connection between the working 
vessel and the auxiliary holder should be made without india-rubber, which is liable 
to be attacked by the ozonized gases. 

The apparatus has been kept in operation for fourteen hours continuously, and 
there should be no difficulty in working day and night. An electric signal could 
easily be arranged to give notice of the extinction of the arc, which sometimes occurs 
unexpectedly ; or an automatic device for re-striking the arc could be contrived. — 
April, 1895.] 

9. Density of Argon prepared by means of Oxygen. 

A first estimate of the density of argon prepared by the oxygen method was 
founded upon the data recorded already respecting the volume present in air, on the 
assumption that the accurately known densities of " atmospheric " and of chemical 
nitrogen differ on account of the presence of argon in the former, and that during the 
treatment with oxygen nothing is oxidised except nitrogen. Thus, if 

D = density of chemical nitrogen, 

D' = ., atmospheric nitrogen, 

d = „ argon, 

a = proportional volume of argon in atmospheric nitrogen, 

the law of mixtures gives 

ad + (1 - a)D = D 

or 

d = D + (D' - D)/a. 



A NEW CONSTITUENT OF THE ATMOSPHERE. 221 

In this formula D' — D and a are both small, but they are known with fair 
accuracy. From the data already given for the experiment of September 8 th 

65 

= 0-0104; 



0-79 x 7925 



whence, if on an arbitrary scale of reckoning D = 2-2990, D' = 2'3102, we find 
d = 3-378. Thus if N 2 be 14, or O, be 16, the density of argon is 20'6. 
AgF.in, from the January experiment, 

4 

75-0 
a= 7^ = °-° 103; 

whence, if N = 14, the density of argon is 20 "6, as before. There can be little doubt, 
however, that these numbers are too high, the true value of a being greater than is 
supposed in the above calculations. 

A direct determination by weighing is desirable, but hitherto it has not been 
feasible to collect by this means sufficient to fill the large globe (§1) employed for 
other gases. A mixture of about 400 cub. centims. of argon with pure oxygen, 
however, gave the weight 27315, 0"1045 in excess of the weight of oxygen, viz., 
2 '6270. Thus, if a be the ratio of the volume of argon to the whole volume, the 
number for ai-gon will be 

2-6270 + 0'1045/a. 

The value of a, being involved only in the excess of weight above that of oxygen, 
does not recpiire to be known very accurately. Sufficiently concordant analyses by two 
methods gave a = - 1845 ; whence, for the weight of the gas we get 3'193 ; so that 
if O = 16, the density of the gas would be 19'45. An allowance for residual nitrogen, 
still visible in the gas before admixture of oxygen, raises this number to 19-7, which 
may be taken as the density of pure argon resulting from this determination.* 

10. Density of Argon Prepared by means of MagnesiumA 

It has already been stated that the density of the residual gas from the first aud 
preliminary attempt to separate oxygen and nitrogen from air by means of mag- 
nesium was 19 - 08 6, and allowing for contraction on sparking with oxygen the density 
is calculable as 20'01. The following determinations of density were also made : — 

(a.) After absorption in glass tubes, the water circulator having been used, and 
subsequent circulation by means of mercury circulator until rate of contraction had 

* [The proportion of nitrogen (4 or o per cent, of the voltime) was estimated from the appearance of 
the nitrogen lines in the spectram, these being somewhat more easily visible than when 3 per cent, 
of nitrogen was introduced into pure argon (§ 8). — April, 1895.] 

t See Addendum, p. 237. 



222 LORD RAYLEIGH AND PROFESSOR W. RAMSAY ON ARGON, 

become slow, 162*843 cub. centims., measured at 7577 millims. (corr.) pressure, and 
16-81° C, weighed 0-2683 grm. Hence, 

Weight of 1 litre at 0° and 760 millims. . . . 17543 grins. 
Density compared with hydrogen (0 = 16) . . 19 "63 ,, 

This gas was again circulated over red-hot magnesium for two days. Before 
circulation it contained nitrogen as was evident from its spectrum ; after circulating, 
nitrogen appeared to be absent, and absorption had completely stopped. The density 
was again determined. 

(b.) 162,843 cub. centims., measured at 745*4 millims. (corr.) pressure, and 
17-25° C, weighed 0-2735 grm. Hence, 

Weight of 1 litre at 0° and 760 millims. . . . 1*8206 grms. 
Density compared with hydrogen (0 = 16) . . 20'38 ,, 

Several portions of this gas, having been withdrawn for various purposes, were 
somewhat contaminated with air, owing to leakage, passage through the pump, &c. 
All these portions were united in the gas-holder with the main stock, and circulated 
for eight hours, during the last three of which no contraction occurred. The gas 
removed from the system of tubes by the mercury-pump was not restored to the 
gas-holder, but kept separate. 

(c.) 162*843 cub. centims., measured at 758*1 millims. (corr.) pressure, and 
17*09° O, weighed 0*27705 grm. Hence, 

Weight of 1 litre at 0° and 760 millims. . . . 1*8124 grms. 
Density compared with hydrogen (O = 16) . . 20*28 ,, 

The contents of the gas-holder were subsequently increased by a mixture of 
nitrogen and argon from 37 litres of atmospheric nitrogen, and after circulating, 
density was determined. The absorption was however not complete. 

(d.) 162*843 cub. centims., measured at 767'6 millims. (corr.) pressure, and 
16*31° O, weighed 0*2703 grm. Hence, 

Weight of 1 litre at 0° and 760 millims 1*742 grms. 

Density compared with hydrogen (O = 16) . . . 19*49 ,, 

The gas was further circulated, until all absorption had ceased. This took about 
six hours. Density was again determined. 

(e.) 1 62*843 cub. centims. measured at 767*7 millims. (corr.) pressure, and 15*00° C, 
weighed 0*2773 grm. Hence, 

Weight of 1 litre at 0° and 760 millims. . . % 1*7784 grms. 
Density compared with hydrogen (0=16) . . 19*90 ,, 



A NEW CONSTITUENT OF THE ATMOSPHERE. 223 

(f.) A second, determination was carried out, without further circulation. 
162*843 cub. centiins. measured at 769'0 millims. (corr.) pressure, and 16'00°C, 
weighed 0*2757 grm. Hence, 

Weight of 1 litre at 0° and 760 millims. . . . 17713 grins. 
Density compared with hydrogen (0 = 16) . . . 19*82 „ 

(g.) After various experiments had been made with the same sample of gas, it was 
again circulated until all absorption ceased. A vacuum-tube was filled with it, and 
showed no trace of nitrogen. 

The density was again determined : — 

162*843 cub. centims. measured at 750 millims. (corr.) pressure, and at 15"62° C, 
weighed 0*26915 grm. 

Weight of 1 litre at 0° and 760 millims. . . . 17707 grms. 
Density compared with hydrogen (0 = 16). . . 19 "82 ,, 

These comprise all the determinations of density made. It should be stated that 
there was some uncertainty discovered later about the weight of the vacuous globe in 
(6) and (c). Rejecting these weighings, the mean of (e), (_/*)_, and (g) is 19 '8 8. The 
density may be taken as 19 "9, with approximate accuracy. 

It is better to leave these results without comment at this point, and to return 
to them later. 

11. Spectrum of Argon. 

Vacuum tubes were filled with argon prepared by means of magnesium at various 
stages in this work, and an examination of these tubes has been undertaken by 
Mr. Crookes, to whom we wish to express our cordial thanks for his kindness in 
affording us helpful information with regard to its spectrum. The first tube was 
filled with the early preparation of density 19*09, which obviously contained some 
nitrogen. A photograph of the spectrum was taken, and compared with a photograph 
of the spectrum of nitrogen, and it was at once evident that a spectrum different from 
that of nitrogen had been registered. 

Since that time many other samples have been examined. 

The spectrum of argon, seen in a vacuum tube of about 3 millims. pressure, consists 
of a great number of lines, distributed over almost the whole visible field. Two lines 
are specially characteristic ; they are less refrangible than the red lines of hydrogen or 
lithium, and serve well to identify the gas when examined in this way. Mr. Crookes, 
who gives a full account of the spectrum in a separate communication, has kindly 
furnished us with the accurate wave-lengths of these lines as well as of some others 
next to be described; they are respectively 696*56 and 705*64 X 10*"° millim. 

Besides these red lines, a bright yellow line, more refrangible than the sodium line, 



224 LORD RAYLEIGH AND PROFESSOR W. RAMSAY ON ARGON, 

occurs at 603'84. A group of five bright green lines occurs next, besides a number of 
less intensity. Of this group of five, the second, which is perhaps the most brilliant, 
has the wave-length 561*00. There is next a blue, or blue-violet, line of wave-length 
470 - 2 and last, in the less easily visible part of the spectrum, there are five strong- 
violet lines, of which the fourth, which is tbe most brilliant, has the wave- 
length 420-0. 

Unfortunately, the red lines, which are not to be mistaken for those of any other 
substance, are only to be seen at atmospheric pressure when a very powerful jar- 
discharge is passed through argon. The spectrum, seen under these conditions, has 
been examined by Professor Schuster. The most characteristic lines are perhaps 
those in the neighbourhood of F, and are very easily seen if there be not too much 
nitrogen, in spite of the presence of some oxygen and water-vapour. The approximate 
wave-lengths are : — 

487-91 Strong. 

(486-07) F. 

484*71 Not quite so strong. 

480'52 Strong. 

476-501 

473 - 53 )> . . . . Fairly strong characteristic triplet. 

472-56 j 

It is necessary to anticipate Mr. Crookes's communication, and to state that when 
the current is passed from the induction-coil in one direction, that end of the capillary 
tube next the positive pole appears of a redder, and that next the negative of a bluer 
hue. There are, in effect, two spectra, which Mr, Crookes has succeeded in separat- 
ing to a considerable extent. Mr. F. C. C. Baly,* who has noticed a similar phe- 
nomenon, attributes it to the presence of two gases. The conclusion would follow that 
what we have termed " argon " is in reality a mixture of two gases which have as yet 
not been separated. This conclusion, if true, is of great importance, and experiments 
are now in progress to test it by the use of other physical methods. The full bearing 
of this possibility will appear later. 

A comparison was made of the spectrum seen in a vacuum tube with the spectrum 
in a "plenum" tube, i.e., one filled at atmospheric pressure. Both spectra were 
thrown into a field at the same time. It was evident that they were identical, 
although the relative strengths of the lines were not always the same. The seventeen 
most striking lines were absolutely coincident. 

The presence of a small quantity of nitrogen interferes greatly with the argon 
spectrum. But we have found that in a tube with platinum electrodes, after the 

* ' Proc. Phys. Soo.,' 1893, p. 147. He says : " When an electric current is passed through a mixture 
of tTvo gases, one is separated from the other, and appears in the negative glow." 



A NEW CONSTITUENT OP THE ATMOSPHERE. 225 

discharge has been passed for four hours, the spectrum of nitrogen disappears, and 
the argon spectrum manifests itself in full purity. A specially constructed tube, with 
magnesium electrodes, which we hoped would yield good results, removed all traces 
of nitrogen it is true, but hydrogen was evolved from the magnesium, and showed its 
characteristic lines very strongly. However, these are easily identified. The gas 
evolved on heating magnesium in vacuo, as proved by a separate experiment, consists 
entirely of hydrogen. 

Mr. Ckookes has proved the identity of the chief lines of the spectrum of gas 
separated from air-nitrogen by aid of magnesium with that remaining after sparking 
air-nitrogen with oxygen, in presence of caustic soda solution. 

Professor Schuster has also found the principal lines identical in the spectra of 
the two gases, when taken from the jar discharge at atmospheric pressure. 

12. Solubility of Argon in Water. 

The tendency of the gas to disappear when manipulated over water in small 
quantities having suggested that it might be more than usually soluble in that liquid, 
special experiments were tried to determine the degree of solubility. 

The most satisfactory measures relating to the gas isolated by means of oxygen 
were those of September 28. The sample contained a trace of oxygen, and (as 
judged by the spectrum) a residue of about 2 per cent, of nitrogen. The procedure 
and the calculations followed pretty closely the course marked out by Bunsen,* and 
it is scarcely necessary to record the details. The quantity of gas operated upon was 
about 4 cub. centims., of which about 1\ cub. centims. were absorbed. The final 
result for the solubility was 3"94 per 100 of water at 12° C, about 2^ times that of 
nitrogen. Similar results have been obtained with argon prepared by means of 
magnesium. At a temperature of 13'9°, 131 arbitrary measures of water absorbed 
5 "3 of argon. This corresponds to a solubility in distilled water, previously freed 
from dissolved gas by boiling in vacuo for a quarter of an hour, and admitted to the 
tube containing argon without contact with air, of 4'05 cub. centims. of argon per 
100 of water. 

The fact that the gas is more soluble than nitrogen would lead us to expect it in 
increased proportion in the dissolved gases of rain water. Experiment has confirmed 
this anticipation. Some difficulty was at first experienced in collecting a sufficiency 
for the weighings in the large globe of nearly 2 litres capacity. Attempts at 
extraction by means of a Topler pump without heat were not very successful. It was 
necessary to operate upon large quantities of water, and then the pressure of the 
liquid itself acted as an obstacle to the liberation of gas from all except the upper 
layers. Tapping the vessel with a stick of wood promotes the liberation of gas in a 

* ' Gasometry,' p. 141. 
MDCCCXCV. — A. 2 G 



226 



LORD RAYLEIGH AND PROFESSOR W. RAMSAY ON ARGON, 



remarkable manner, but to make this method effective, some means of circulating the 
water would have to be introduced. 

The extraction of the gases by heat proved to be more manageable. Although a 
large quantity of water has to be brought to or near 100° C, a prolonged boiling is 
not necessary, as it is not a question of collecting the whole of the gas contained in 
the water. The apparatus employed, which worked very well after a little experience, 
will be understood from the accompanying figure. The boiler A was constructed 



Fig. 8. 





from an old oil-can, and was heated by an ordinary ring Bunsen burner. For the 
supply and removal of water, two co-axial tubes of thin brass, and more than four feet 
in length, were applied upon the regenerative principle. The outgoing water flowed 
in the inner tube BC, continued from C to D by a prolongation of composition 
tubing. The inflowing water from a rain-water cistern was delivered into a glass 
tube at E, and passed through a brass connecting tube FG into the narrow annular 
space between the two principal tubes GH. The neck of the can was fitted with an 
india-rubber cork and delivery-tube, by means of which the gases were collected in 



A NEW CONSTITUENT OF THE ATMOSPHERE. 227 

the ordinary way. Any carbonic anhydride was removed by alkali before passage 
into the glass aspirating bottles used as gas-holders. 

The convenient working of this apparatus depends very much upon the mainten- 
ance of a suitable relation between the heat and the supply of water. It is desirable 
that the water in the can should actually boil, but without a great development of 
steam ; otherwise not only is there a waste of heat, and thus a smaller yield of gas, 
but the inverted flask used for the collection of the gas becomes inconveniently hot and 
charged with steam. It was found desirable to guard against this by the application 
of a slow stream of water to the external surface of the flask. When the supply of 
water is once adjusted, nearly half a litre of gas per hour can be collected with very 
little attention. 

The gas, of which about four litres are required for each operation, was treated 
with red-hot copper, cupric oxide, sulphuric acid, potash, and finally phosphoric anhy- 
dride, exactly as atmospheric nitrogen was treated in former weighings. The weights 
found, corresponding to those recorded in § 1, were on two occasions, 2 - 3221 and 
2"3227, showing an excess of 24 milligrms. above the weight of true nitrogen. Since 
the corresponding excess for atmospheric nitrogen is 11 milligrms., we conclude 
that the water-nitrogen is relatively twice as rich in argon. 

Unless some still better process can be found, it may be desirable to collect the 
gases ejected from boilers, or from large supply pipes which run over an elevation, 
with a view to the preparation of argon upon a large scale. 

The above experiments relate to rain water. As regards spring water, it is known 
that many thermal springs emit considerable quantities of gas, hitherto regarded as 
nitrogen. The question early occurred to us as to what proportion, if any, of the 
new gas was contained therein. A. notable example of a nitrogen spring is that at 
Bath, examined by Datjbejty in 1833. With the permission of the authorities of 
Bath, Dr. Arthtj.r Rickabdson was kind enough to collect for us about 10 litres of 
the gases discharged from the King's Spring. A rough analysis on reception showed 
that it contained scarcely any oxygen and but little carbonic anhydride. Two 
determinations of density were made, the gas being treated in all respects as air. 
prepared by diffusion and unprepared, were treated for the isolation of atmospheric 
nitrogen. The results were : — 

October 29 2-30513 

November 7 2"30532 

Mean 2-30522 

The weight of the "nitrogen" from the Bath gas is thus about halfway between 
that of chemical and "atmospheric" nitrogen, suggesting that the proportion of 
argon is less than in air, instead of greater as had been expected. 

2 G 2 



228 



LORD RAYLEIGH AND PROFESSOR W. RAMSAY ON ARGON, 



13. Behaviour at Low Temperatures. 

A single experiment was made with an early sample of gas, of density 19*1, 
which certainly contained a considerable amount of nitrogen. On compressing it in a 
pressure apparatus to between 80 and 100 atmospheres pressure, and cooling to 
— 90° by means of boiling nitrous oxide, no appearance of liquefaction could be 
observed. As the critical pressure was not likely to be so high as the pressure to 
which it had been exposed, the non-liquefaction was ascribed to insufficient cooling. 

This supposition turned out to be correct. For, on sending a sample to Professor 
Olszewski, the author of most of the accurate measurements of the constants of 
gases at low temperatures, he was kind enough to submit it to examination. His 
results are published elsewhere ; but, for convenience of reference, his tables, showing 
vapour-pressures, and giving a comparison between the constants of argon and those 
of other gases, are here reproduced. 

Vapotjr-presstjr.es. 



Temperature. 


Pressure. Temperature. 


Pressure. Temperature. 


Pressure. 


- 186-9 

- 1391 

- 138-3 


740'5 millims. 
23'7 atms. 
253 „ 


- 136-2 

- 135-] 

- 134-4 


27-3 atms. - 129°4 
29-0 „ - 128-6 
29-8 „ - 121-0 


35'8 atms. 
38-0 „ 
50-6 „ 



Gas. 


Critical 
tempera- 
ture. 


Critical 
pressure. 


Boiling- 
point. 


Freezing- 
point. 


Freezing 
pressure. 


Density 
of gas. 


Density 
of liquid 
at boiling- 
point. 


Colour of 
liquid. 


Hydrogen, H, . . . 

Nitrogen, N 3 . . . . 
Carbon monoxide, CO 
Argon, Aj 

Oxygen, 0. 2 . . . . 
Nitric oxide, NO . . 
Methane, CH 4 . . . 


Below 

-220-0° 
-1460 
-1395 
-1210 

-118-8 

- 935 

- 81-8 


atms. 
20-0 

35-0 
35-5 
506 

50-8 
7T2 
54-9 


? ° 

-194-4 
-190-0 
-186-9 

-182-7 
-153-6 
-164-0 


o 

p 

-214-0 
-207-0 
-189-6 

? 
-167-0 
-185-8 


millims. 
? 

60 
100 

? 

? 

138 

80 


1 

14 
14 
19-9 

16 
15 

8 


? 

0-885 
? 

About 
1-5 
1124 

? 

0-415 


Colourless 

?> 

J! 

Bluish 
Colourless 

1 



14. TJie ratio of the Specific Heats of Argon* 

In order to decide regarding the elementary or compound nature of argon, 
experiments were made on the velocity of sound in it. It will be remembered that 
from the velocity of sound, the ratio of the specific heat at constant pressure to that 
at constant volume can be deduced by means of the equation 

* See Addendum, p. 239. 



A NEW CONSTITUENT OF THE ATMOSPHERE. 229 

where n is the frequency, \ is the wave-length of sound, v its velocity, e the 
isothermal elasticity, d the density, (1 + a-t) the temperature-correction, C p the 
sjiecific heat at constant pressure, and C„ that at constant volume. In comparing 
two gases at the same temperature, each of which obeys Boyle's law with sufficient 
approximation and in using the same sound, many of these factors disappear, and the 
ratio of specific heats of one gas may be deduced from that of the other, if known, 
by the simple proportion 

\"d :\ ,ji d' : : 1-408 : x, 

where for example A. and d refer to air, of which the ratio is 1*408, according to 
the mean of observations by Rontgen (1*4053), Wullner (1*4053), Kayser (1*4106), 
and Jamin and Richard (1*41). 

The apparatus employed, although in principle the same as that usually employed, 
differed somewhat from the ordinary pattern, inasmuch as the tube was a narrow one, 
of 2 millims. bore, and the vibrator consisted of a glass rod, sealed into one end of 
the tube, so that about 15 centims. projected outside the tube, while 15 centims. was 
contained in the tube. By rubbing the projecting part longitudinally with a rag wet 
with alcohol, vibrations of exceedingly high pitch of the gas contained in the tube 
took place, causing waves which registered their nodes by the usual device of 
lycopodium powder. The temperature was that of the atmosphere and varied little 
from 17*5°; the pressure was also atmospheric, and varied only one millim. during 
the experiments. Much of the success of these experiments depends on so adjusting 
the length of the tube as to secure a good echo, else the wave-heaps are indistinct. 
But this is easily secured by attaching to its open end a piece of thick-walled india- 
rubber tubing, which can be closed by a clip at a spot which is found experimentally 
to produce good heaps at the nodes. 

The accuracy of this instrument has frequently been tested ; but fresh experiments 
were made with air, carbon dioxide, and hydrogen, so as to make certain that 
reasonably reliable results were obtainable. Of these an account is here given. 



Gas in tube. 


Number of observations. 


Half- wave-length. 


Ratio ^ . 

KJD 


I. 


II. 


I. 


II. 


Air .... 
CO,. . . . 
H, . . . . 


3 
3 
3 


2 

" 


19-60 
1511 

73-6 


19-59 


1-408 Assumed 
1-276 Found 
1-376 Found 



To compare these results with those of previous observers, the following numbers 



230 



LORD RATLEIGH AND PROFESSOR W. RAMSAY ON ARGON, 



were obtained for carbon dioxide: — Cazin, 1 - 29L; Rontgen, 1-305; De Lucchi, 
1-292; Muller, 1-265; Wullner, 1-311; Dulong, 1-339; Masson, 1'274; Reg- 
natjlt, l - 268; Amagat, 1-299 ; and Jamin and Richard, 1*29. It appears just to 
reject Dulong's number, which deviates so markedly from the rest ; the mean of 
those remaining is 1*288, which is in sufficient agreement with that given above. 
For the ratio of the specific heats of hydrogen, we have : — Cazin, 1*410 ; Rontgen, 
1*385 ; Dulong, 1*407 ; Masson, 1*401 ; Regnatjlt, 1*400 ; and Jamin and Richard, 
1*410. The mean of these numbers is 1*402. This number appears to differ con- 
siderably from the one given above. But it must be noted, first, that the wave- 
length which should have been found is 74*5, a number differing but little from that 
actually found ; second, that the waves were long and that the nodes were somewhat 
difficult to place exactly ; and third, that the atomic weight of hydrogen has been 
taken as unity, whereas it is more likely to be 1*01, if oxygen, as was done, be taken 
as 16. The atomic weight 1*01 raises the found value of the ratio to 1*399, a number 
differing but little from the mean value found by other observers. 

Having thus established the trustworthiness of the method, we proceed to describe 
our experiments with argon. 

Five series of measurements were made with the sample of gas of density 19 -82. 
It will be remembered that a previous determination with the same gas gave as its 
density 19*90. The mean of these two numbers was therefore taken as correct, 
viz., 19-86. 

The individual measurements are : — 



1. 


II. 


III. 


IV. 


V. 


Mean. 


18-16 


18-14 


18-02 


18-04 


1803 


millims. 
18-08 



for the half-wave-length. Calculating the ratio of the specific heats, the number 
1-644 is obtained. 

The narrowness of the tube employed in these experiments might perhaps raise a 
doubt regarding the accuracy of the measurements, for it is conceivable that in 
so narrow a tube the viscosity of the gas might affect the results. We therefore 
repeated the experiments, using a tube of 8 millims. internal diametei*. 

The mean of eleven readings with air, at 18°, gave a half- wave Jength of 
34*62 millims. With argon in the same tube, and at the same temperature, the 
half-wave-length was, as a mean of six concordant readings, 31*64 millims. The 
density of this sample of argon, which had been transferred from a water gas-holder 
to a mercury gas-holder, was 19*82 ; and there is some reason to suspect the presence 
of a trace of ah*, for it had been standing for some time. 

The result, however, substantially proves that the ratio previously found was 



A NEW CONSTITUENT OF THE ATMOSPHERE. 231 

correct. In the wide tube, C^ : C„ : : 1 - 61 : 1. Hence the conclusion must be 
accepted that the ratio of specific heats is practically 1'66 : 1. 

It will be noticed that this is the theoretical ratio for a monatomic gas, that is, a 
gas in which all energy imparted to it at constant volume is expended in effecting 
translational motion. The only other gas of which the ratio of specific heats has 
been found to fulfil this condition is mercury at a high temperature.* The extreme 
importance of these observations will be discussed later. 

15. Attempts to induce Chemical Combination. 

A great number of attempts were made to induce chemical combination with 
the argon obtained by use of magnesium, but without any positive result. In such a 
case as this, however, it is necessary to chronicle negative results, if for no other 
reason but that of justifying its name, " argon." These will be detailed in order. 

(a) Oxygen in Presence of Caustic Alkali. — This need not be further discussed 
here ; the method of preparing argon is based on its inactivity under such con- 
ditions. 

(b) Hydrogen. — It has been mentioned that, in order to free argon from excess of 
oxygen, hydrogen was admitted, and sparks passed to cause combination of hydrogen 
and oxygen. Here again caustic alkali was present, and argon appeared to be 
unaffected. 

A separate experiment was, however, made in absence of water, though no special 
pains was taken to dry the mixture of gases. The argon was admitted up to half an 
atmosphere pressure into a bulb, through whose sides passed platinum wires, carrying 
pointed poles of gas-carbon. Hydrogen was then admitted until atmospheric pressure 
had been attained. Sparks were then passed for four hours by means of a large 
induction coil, actuated by four storage cells. The gas was confined in a bulb closed 
by two stop-cocks, and a small V-tube with bulbs was interposed, to act as a gauge, 
so that if expansion or contraction had taken place, the escape or entry of gas would 
be observable. The apparatus, after the passage of sparks, was allowed to cool to 
the temperature of the atmosphere, and, on opening the stop-cock, the level of water 
in the V-tube remained unaltered. It may therefore be concluded that, in all 
probability, no combination has occurred ; or, that if it has, it was attended with no 
change of volume. 

(c) Chlorine. — Exactly similar experiments were performed with dry, and after- 
wards with moist, chlorine. The chlorine had been stored over strong sulphuric acid 
for the first experiment, and came in contact with dry argon. Three hours sparking 
produced no change of volume. A drop of water was admitted into the bulb. After 
four hours sparking, the volume of the gas, after cooling, was diminished by about 

* Kundt and Warburg, ' Pogg. Ann.,' 157, p. 353, 1876. 



232 LORD RAYLE1GH AND PROFESSOR W. RAMSAY ON ARGON, 

Yo cub. centini., due probably to the solution of a little chlorine in the small quantity 
of water present. 

(d) Phosphorus. — A piece, of combustion-tubing, closed at one end, containing at 
the closed end a small piece of phosphorus, was sealed to the mercury reservoir 
containing argon ; connected to the same reservoir was a mercury gauge and a 
Sprengel's pump. After removing all air from the tubes, argon was admitted to a 
pressure of 600 millims. The middle portion of the combustion-tube was then heated 
to bright redness, and the phosphorus was distilled slowly from back to front, so that 
its vapour should come into contact with argon at a red heat. When the gas was hot, 
the level of the gauge altered ; but, on cooling, it returned to its original level, 
showing that no contraction had taken place. The experiment was repeated several 
times, the phosphorus being distilled through the red-hot tube from open to closed 
end, and vice versa. In each case, on cooling, no change of pressure was remarked. 
Hence it may be concluded that phosphorus at a red-heat is without action on argon. 
It may be remarked parenthetically that no gaseous compound of phosphorus is 
known, which does not possess a volume different from the sum of those of its 
constituents. That no solid compound was formed is sufficiently proved by the 
absence of contraction. The phosphorus was largely converted into the red modifica- 
tion during the experiment. 

(e) Sulphur. — An exactly similar experiment was performed with sulphur, again 
with negative results. It may therefore be concluded that sulphur and argon are 
without action on each other at a red heat. And again, no gaseous compound of 
sulphur is known in which the volume of the compound is equal to the sum of those 
of its constituents. 

(/') Tellurium. — As this element has a great tendency to unite with heavy metals, 
it was thought worth while to try its action. In this, and in the experiments to be 
described, a different form was given to the apparatus. The gas was circulated over 
the reagent employed, a tube containing it being placed in the circuit. The gas was 
dried by passage over soda-lime and phosphoric anhydride ; it then passed over the 
tellurium or other reagent, then through drying tubes, and then back to the gas- 
holder. That combination did not occur was shown by the unchanged volume of gas 
in the gas-holder ; and it was possible, by means of the graduated cylinder which 
admitted water to the gas-holder, to judge of as small an absorption as half a cubic 
centimeter. The tellurium distilled readily in the gas, giving the usual yellow 
vapours ; and it condensed, quite unchanged, as a black sublimate. The volume of 
the g - as, when all was cold, was unaltered. 

(g) Sodium. — A piece of sodium, weighing about half a gramme, was heated in argon. 
It attacked the glass of the combustion tube, which it blackened, owing to liberation 
of silicon ; but it distilled over in drops into the cold part of the tube. Again no 
change of volume occurred, nor was the surface of the distilled sodium tarnished ; it 
was brilliant, as it is when sodium is distilled in vacuo. It may probably also be 



A NEW CONSTITUENT OF THE ATMOSPHERE. 233 

concluded from this experiment that silicon, even while being liberated, is without 
action on argon. 

The action of compounds was then tried ; those chosen were such as lead to oxides 
or sulphides. Inasmuch as the platinum-metals, which are among the most inert of 
elements, are attacked by fused caustic soda, its action was investigated. 

(h) Fused and Red-hot Caustic Soda. — The soda was prepared from sodium, in an 
iron boat, by adding drops of water cautiously to a lump of the metal. When action 
had ceased, the soda was melted, and the boat introduced into a piece of combustion- 
tube placed in the circuit. After three hours circulation no contraction had occurred. 
Hence caustic soda has no action on argon. 

(?■) Soda-lime at a red-heat. — Thinking that the want of porosity of fused caustic 
soda might have hindered absorption, a precisely similar experiment was carried out 
with soda-lime, a mixture which can be heated to bright redness without fusion. 
Again no result took place after three hours heating. 

(j) Fused Potassium Nitrate was tried under the impression that oxygen plus a 
base might act where oxygen alone failed. The nitrate w r as fused, and kept at a 
bright red heat for two hours, but again without any diminution in volume of the 
argon. 

(£) Sodium Peroxide. — Yet another attempt was made to induce combination with 
oxygen and a base, by heating sodium peroxide to redness in a current of argon for 
over an hour, but also without effect. It is to be noticed that metals of the platinum 
group would have entered into combination under such treatment. 

(/) Persidphides of Sodium and Calcium.- — Soda-lime was heated to redness in 
an open crucible, and some sulphur was added to the red-hot mass, the lid of the 
crucible being then put on. Combination ensued, with formation of polysulphides 
of sodium and calcium. This product was heated to redness for three hours in a 
brisk current of argon, again with negative result. Again, metals of the platinum 
group would have combined under such treatment. 

(m) Some argon was shaken in a tube with nitro-hydrochloric acid. On addition 
of potash, so as to neutralise the acid, and to absorb the free chlorine and nitrosyl 
chloride, the volume of the gas was barely altered. The slight alteration was evidently 
due to solubility in the aqueous liquid, and it may be concluded that no chemical 
action took place. 

(n) Bromine-water was also without effect. The bromine vapour was removed 
with potash. 

(o) A mixture of potassium permanganate and hydrochloric acid, involving the 
presence of nascent chlorine, had no action, for on absorbing chlorine by means of 
potash, no alteration in volume had occurred. 

(p) Argon is not absorbed by platinum black. A current was passed over a pure 
specimen of this substance ; as usual, however, it contained occluded oxygen. There 
was no absorption in the cold. At 100°, no action took place ; and on heating to 

MDCCCXCV. — A. 2 H 



234 LORD RAYLETGH AND PROFESSOR W. RAMSAY ON ARGON, 

redness, by which the black was changed to sponge, still no evidence of absorption 
was noticed. In all these experiments, absorption of half a cubic centimetre of argon 
could have at once been detected. 

We do not claim to have exhausted the possible reagents. But this much is 
certain, that the gas deserves the name " argon," for it is a most astonishingly indif- 
ferent body, inasmuch as it is unattached by elements of very opposite character, 
ranging from sodium and magnesium on the one hand, to oxygen, chlorine, and 
sulphur on the other. It will be interesting to see if fluorine also is without action, 
but for the present that experiment must be postponed, on account of difficulties of 
manipulation. 

It will also be necessary to try whether the inability of argon to combine at 
ordinary or at high temperatures is due to the instability of its possible compounds, 
except when cold. Mercury vapour at 800° would present a similar instance of 
passive behaviour. 

16. General Conclusions. 

It remains, finally, to discuss the probable nature of the gas or gases which we 
have succeeded in separating from atmospheric air, and which has been provisionally 
named argon. 

That argon is present in the atmosphere, and is not manufactured during the 
process of separation is amply proved by many lines of evidence. First, atmospheric 
nitrogen has a high density, while chemical nitrogen is lighter. That chemical 
nitrogen is a uniform substance is proved by the identity of properties of samples 
prepared by several different processes, and from several different compounds. It 
follows, therefore, that the cause of the high density of atmospheric nitrogen is due 
to the admixture with heavier gas. If that gas possesses the density of 20 compared 
with hydrogen as unity, atmospheric nitrogen should contain of it approximately 
1 per cent. This is found to be the case, for on causing the nitrogen of the atmos- 
phere to combine with oxygen in presence of alkali, the residue amounted to about 
1 per cent. ; and on removing nitrogen with magnesium the result is similar. 

Second : This gas has been concentrated in the atmosphere by diffusion. It is true 
that it cannot be freed from oxygen and nitrogen by diffusion, but the process of 
diffusion increases relatively to nitrogen the amount of argon in that portion which 
does not pass through the porous walls. That this is the case is proved by the 
increase of density of that mixture of argon and nitrogen. 

Third : On removing nitrogen from " atmospheric nitrogen " by means of magne- 
sium, the density of the residue increases proportionately to the concentration of the 
heavier constituent. 

Fourth : As the solubility of argon in water is relatively high, it is to be expected 
that the density of the mixture of argon and nitrogen, pumped out of water 
along with oxygen should, after removal of the oxygen, exceed that of "atmos- 
pheric nitrogen." Experiment has shown that the density is considerably increased. 



A NEW CONSTITUENT OF THE ATMOSPHERE. 235 

Fifth : It is in the highest degree improbable that two processes, so different from 
each other, should each manufacture the same product. The explanation is simple if 
it be granted that these processes merely eliminate nitrogen from " atmospheric 
nitrogen." 

Sixth : If the newly discovered gas were not in the atmosphere, the discrepancies 
in the density of " chemical " and " atmospheric " nitrogen would remain unexplained. 

Seventh : It has been shown that pure nitrogen, prepared from its compounds, 
leaves a negligible residue when caused to enter into combination with oxygen or 
with magnesium. 

There are other lines of argument which suggest themselves ; but we think that it 
will be acknowledged that those given above are sufficient to establish the existence 
of argon in the atmosphere. 

It is practically certain that the argon prepared by means of electric sparking with 
oxygen is identical with argon prepared by means of magnesium. The samples have 
in common : — 

First : Spectra which have been found by Mr. Crook.es, Professor Schuster, and 
ourselves to be practically identical. 

Second : They have approximately the same density. The density of argon, pre- 
pared by means of magnesium, was 19 "9 ; that of argon, from sparking with oxygen, 
about 1 9 '7 ', these numbers are practically identical. 

Third : Then solubility in water is the same. 

That argon is an element, or a mixture of elements, may be inferred from the 
observations of § 14. For Clausius has shown that if K be the energy of translatory 
motion of the molecules of a gas, and H their whole kinetic energy, then 

k_ 3 (c, - o 

H 20, 

ij p and C denoting as usual the specific heat at constant pressure and at constant 
volume respectively. Hence, if, as for mercury vapour and for argon (§ 14), the 
ratio of specific heats C p : C s be If, it follows that K = H, or that the whole kinetic 
energy of the gas is accounted for by the translatory motion of its molecules. In the 
case of mercury the absence of interatomic energy is regarded as proof of the mon- 
atomic character of the vapour, and the conclusion holds equally good for argon. 

The only alternative is to suppose that if argon molecules are di- or polyatomic, 
the atoms acquire no relative motion, even of rotation, a conclusion improbable in 
itself and one postulating the sphericity of such complex groups of atoms. 

Now a monatomic gas can be only an element, or a mixture of elements ; and 
hence it follows that argon is not of a compound nature. 

According to Avogadro, equal volumes of gases at the same temperature and 
pressure, contain equal numbers of molecules. The molecule of hydrogen gas, the 
density of which is taken as unity, is supposed to consist of two atoms. Its mole- 

2 H 2 



236 LORD RAYLEIGH AND PROFESSOR W. RAMSAY ON ARGON, 

cular weight is therefore 2. Argon is approximately 20 times as heavy as hydrogen, 
that is, its molecular weight is 20 times as great as that of hydrogen, or 40. But its 
molecule is monatomic, hence its atomic weight, or, if it be a mixture, the mean of 
the atomic weights of the elements in that mixture, taken for the proportion in which 
they are present, must he 40. 

This conclusion rests on the assumption that all the molecules of argon are mon- 
atomic. The result of the first experiment is, however, so nearly that required by 
theory, that there is room for only a small number of molecules of a different 
character. A study of the expansion of argon by heat is proposed, and would 
doubtless throw light upon this question. 

There is evidence both for and against the hypothesis that argon is a mixture : for, 
owing to Mr. Grookes's observations of the dual character of its spectrum ; against, 
because of Professor Olszewski's statement that it has a definite melting-point, a 
definite boiling-point, and a definite critical temperature and pressure ; and because 
on compressing the gas in presence of its liquid, pressure remains sensibly constant 
until all gas has condensed to liquid. The latter experiments are the well-known 
criteria of a pure substance ; the former is not known Avith certainty to be character- 
istic of a mixture. The conclusions which follow are, however, so stai'tling, that in 
our future experimental work we shall endeavour to decide the question by other 
means. 

For the present, however, the balance of evidence seems to point to simplicity. 
We have, therefore, to discuss the relations to other elements of an element of atomic 
weight 40. We inclined for long to the view that argon was possibly one, or more 
than one, of the elements which might be expected to follow fluorine in the periodic 
classification of the elements — elements which should have an atomic weight between 
] 9, that of fluorine, and 23, that of sodium. But this view is apparently put out of 
court by the discovery of the monatomic nature of its molecules. 

The series of elements possessing atomic weights near 40 are : — 

Chlorine 35 '5 

Potassium 39*1 

Calcium 40 "0 

Scandium ...... 44 "0. 

There can be no doubt that potassium, calcium, and scandium follow legitimately 
their predecessors in the vertical columns, lithium, beryllium, and boron, and that 
they are in almost certain relation with rubidium, strontium, and (but not so 
certainly) yttrium. If argon be a single element, then there is reason to doubt 
whether the periodic classification of the elements is complete ; whether, in fact, 
elements may not exist which cannot be fitted among those of which it is composed. 
On the other hand, if argon be a mixture of two elements, they might find place in 
the eighth group, one after chlorine and one after bromine. Assuming 37 Cthe 



A NEW" CONSTITUENT OF THE ATMOSPHERE. 237 

approximate mean between the atomic weights of chlorine and potassium) to be the 
atomic weight of the lighter element, and 40 the mean atomic weight found, and 
supposing that the second element has an atomic weight between those of bromine, 
80, and rubidium, 85*5, viz., 82, the mixture should consist of 93 - 3 per cent, of the 
lighter, and 67 per cent, of the heavier element. But it appears improbable that 
such a high percentage as 6 "7 of a heavier element should have escaped detection 
during liquefaction. 

If the atomic weight of the lighter element were 38, instead of 37, however, the 
proportion of heavier element would be considerably reduced. Still, it is difficult tc 
account for its not having been detected, if present. 

If it be supposed that argon belongs to the eighth group, then its properties would 
fit fairly well with what might be anticipated. For the series, which contains 

Si, t IV , P 4 IIIanav , S^ Vi , andCL ItoVn , 

might be expected to end with an element of monatomic molecules, of no valency, i.e., 
incapable of forming a compound, or if forming one, being an octad ; and it would 
form a possible transition to potassium, with its monovalence, on the other hand. 
Such conceptions are, however, of a speculative nature ; yet they may be perhaps 
excused, if they in any way lead to experiments which tend to throw more light on 
the anomalies of this curious element. 

In conclusion, it need excite no astonishment that argon is so indifferent to reagents. 
For mercury, although a monatomic element, forms compounds which are by no means 
stable at a high temperature in the gaseous state ; and attempts to produce compounds 
of argon may be likened to attempts to cause combination between mercury gas at 
800° and other elements. As for the physical condition of argon, that of a gas, we 
possess no knowledge why carbon, with its low atomic weight, should be a solid, while 
nitrogen is a gas, except in so far as we ascribe molecular complexity to the former 
and comparative molecular simplicity to the latter. Argon, with its comparatively 
low density and its molecular simplicity, might well be expected to rank among the 
gases. And its inertness, which has suggested its name, sufficiently explains why it 
has not previously been discovered as a constituent of compound bodies. 

We would suggest for this element, assuming provisionally that it is not a mixture, 
the symbol A. 

We have to record our thanks to Messrs. Gordon, Kellas, and Matthews, and 
especially to Mr. Percy Williams, for their assistance in the prosecution of this 
research. 

Addendum (by Professor W. Bamsay). 

March 20, 1895. 

Further determinations of the density of argon prepared by means of magnesium 
have been made. In each case the argon was circulated over magnesium for at least 



238 



LORD RATLEIGH AND PROFESSOR W. RAMSAY ON ARGON, 



two hours after all absorption of nitrogen had stopped, as well as over red-hot 

copper, copper oxide, soda-lime, and phosphoric anhydride. The gas also passed out 

of the mercury gas-holder through phosphoric anhydride into the weighing globe. 

The results are in complete accordance with previous determinations of density ; and 

for convenience of reference the former numbers are included in the table which 

follows. 

Density of Argon. 













Weight of 




Date. 


Volume. 


Temperature. 


Pressure. 


Weight. 


1 litre at 

0° and 760 

niillims. 


Density 
(0 = 16). 




cub. centinis. 




niillims. 


grm. 






(1) Nov. 26 . . . 


162-843 


15-00 


767-7 


0-2773 


1-7784 


19-904 


(2) „ 27. . . 


162843 


16-00 


769-0 


0-2757 


1-7717 


19-823 


(3) Dec. 22 . . . 


162-843 


15-62 


7501 


0-26915 


1-7704 


19-816 


(4) Feb. 16 . . . 


162843 


13-45 


771-1 


0-2818 


1-7834 


19-959 


(5) „ 19. . . 


162-843 


14-47 


768-2 


0-2789 


1-7842 


19-969 


(6) „ 24. . . 


162-843 


17-85 


764-4 


0-2738 


1-7810 


19-932 



The general mean is 19'900 ; or if Nos. (2) and (3) be rejected as suspiciously low, 
the mean of the remaining four determinations is 19'941. The molecular weight may 
therefore be taken as 39 '9 without appreciable error. 

The value of R in the gas-equation R = pv/T has also been determined between 
— 89° and + 248°. For this purpose, a gas-thermometer was filled with argon, and 
a direct comparison was made with a similar thermometer filled Avith hydrogen. 

The method of using such a hydrogen-thermometer has already been described by 
Ramsay and Shields.""" For the lowest temperature, the thermometer bulbs were 
immersed in boiling nitrous oxide; for atmospheric temperature, in running water; 
for temperatures near 100° in steam, and for the remaining temperatures, in the 
vapours of chlorobenzene, aniline, and quinolene. 

The results are collected in the following tables : — 

Hydrogen Thermometer. 



Temperature. 


Pressure. 


Volume (corr.). 


R. 


° 0. 


millims. 






13-04 


7636 


100036 


2-6705 


9984 


9926 


1-00280 


2-6697 


13062 


1073-8 


1-00364 


2-6701 


185-46 


1218-5 


1-00518 


2-6716 


24866 


1385-1 


1-00703 


2-6737 


- 87-92 


497-3 


0-99756 


2-6804 



* ' Trans. Chem. Soc.,' vol. 63, pp. 835, 836. It is to be noticed that the value of R is not involved 
in using the hydrogen-thermometer; its constancy alone is postulated. 



A NEW CONSTITUENT OF THE ATMOSPHERE. 



239 



The value of R is thus practically constant, and this affords a proof that the four 
last temperatures have been estimated with considerable accuracy. 

Argon Thermometer. 





Temperature. 


Pressure. 


Volume (corr.). 


R. 




°C. 


millims. 






Series I. . . 


1415 


701-7 


1-000396 


2-4446 




14-27 


699-7 


1-000401 


2-4366 




14-40 


702-6 


1-000404 


2-4462 




99-96 


906-5 


1-00280 


2-4379 




100-06 


904-8 


1-00280 


2-4322 




-87-92 


455-6 


0-99756 


2-4556 


By mischance, air leaked into the bulb ; it was therefore refilled. 


Series II. 


130-58 


1060-0 


1-0037 


2-6363 




185-46 


1200 3 


1-0052 


2-6317 


A bubble of argon leaked into the bulb, and the value of R increased. 


Series III. . 


12-05 


760-9 


1-00034 


2-6698 




12-61 


761-3 


1-00034 


2-6728 




248-66 


1384-0 


1-0070 


2-6717 




248-66 


1376-9 


1-0070 


2-6580 




-87-92 


495-7 


0-99756 


26718 



It may be concluded from these numbers, that argon undergoes no molecular 
change between — 88° and + 250°. 

Further determinations of the wave-length of sound in argon have been made, the 
wider tube having been used. In every case the argon was as carefully purified as 
possible. In experiment (3) too much lycopodium dust was present in the tube ; 
that is perhaps the cause of the low result. For completeness' sake, the original 
result in the narrow tube has also been given. 



Date. 


Density. 


Half -wave-length. 


Temperature. 


Ratio. 


In air. 


In argon. 


Air. 


Argon. 


Dec. 6 

„ 20 

Mar. 19 


1992 
19-96 
19 97 
19-94 


19-59 
33-73 
34-10 
34-23 


18-08 
31-00 
31-31 
31-68 


o 

17-5 

6-7 

7-22 
11-20 


o 

17-5 
6-5 

8-64 
11-49 


1-644 
1-641 
1-629 
1-659 



The general mean of these numbers is T643 ; if (3) be rejected, it is 1'648. In 
the last experiment every precaution was taken. The half-wave-length in air is 
the mean of 11 readings, the highest of which was 34 - 67 and the lowest 34 - 00. 
They run : — 



240 LORD RATLE1GH AND PROFESSOR W. RAMSAY ON ARGON, 

34-67 ; 34-06 ; 34-27 ; 34'39 ; 34'00; 34-00; 34-13; 34-20; 34-20; 34'33; 34"33. 
11-25°; 11-00°; 10'80°; 108° ; 10-0°; 11-0° ; 11-3° ; 1T4 ; 11-4° ; 11-6° ; 11-6°. 

With argon the mean is also that of 11 readings, of which the highest is 3T83, 
and the lowest, 31 "5. They are : — 

31-5 ; 31-5 ; 31-66 ; 31-55 ; 31-83 ; 31-77 ; 31-81 ; 31-83; 31*83; 31-50; 31"66. 
11-8°; 11-8°; 1T20 ; 11-40°; 1T60 ; 11'40°; 11-40°; 11-4°; 11-5°; 11-5° ; 11-4°. 

If the atomic weight of argon is identical with its molecular weight, it must closely 
approximate to 39 "9. But if there were some molecules of A 3 present, mixed with a 
much larger number of molecules of A L , then the atomic Aveight would be corres- 
pondingly reduced. Taking an imaginary case, the question may be put : — What 
percentage of molecules of A 3 would raise the density of Aj from 19'0 to 19 - 9 ? A 
density of 19 - would imply an atomic weight of 38'0, and argon would fall into the 
gap between chlorine and potassium. Calculation shows that in 10,000 molecules, 
474 molecules of A 3 would have this result, the remaining 9526 molecules being 
those of Aj. 

Now if molecules of A 3 be present, it is reasonable to suppose that their number 
would be increased by lowering the temperature, and diminished by heating the gas. 
A larger change,-:of density should ensue on lowering than on raising the temperature, 
however, as oh*" the above supposition, there is not a large proportion of molecules of 
A 2 present. 

But it must be acknowledged that the constancy of the found value of R is not 
favourable to this supposition. 

A similar calculation is possible for the ratio of specific heats. Assuming the gas 
to contain 5 per cent, of molecules of A 3 , and 95 per cent, of molecules of A x the 
value of y, the ratio of specific heats, would be 1'648. All that can be said on this 
point is, that the found ratio approximates to this number ; but wdiether the results 
are to be trusted to indicate a unit in the second decimal appears to me doubtful. 

The question must therefore for the present remain open. 

Addendum. 

April 9. 

It appears worth while to chronicle an experiment of which an accident prevented 
the completion. It may be legitimately asked, Does magnesium not absorb any 
argon, or any part of what we term argon ? To decide this question, about 
500 grins, of magnesium nitride, mixed with metallic magnesium which had 
remained unacted on, during extraction of nitrogen from " air-nitrogen," was placed 
in a flask, to which a reservoir full of dilute hydrochloric acid was connected. The 



A NEW CONSTITUENT OF THE ATMOSPHERE. 241 

flask was coupled with a tube full of red-hot copper oxide, intended to oxidise the 
hydrogen which would be evolved by the action of the hydrochloric acid on the 
metallic magnesium. To the end of the copper-oxide tube a gas-holder was attached, 
so as to collect any evolved gas : and the system was attached to a vacuum-pump, in 
order to exhaust the apparatus before commencing the experiment, as well as to 
collect ail gas which should be evolved, and remain in the flask. 

On admitting hydrochloric acid to the flask of magnesium nitride a violent 
reaction took place, and fumes of ammonium chloride passed into the tube of copper 
oxide. These gave, of course, free nitrogen. This had not been foreseen ; it would 
have been well to retain these fumes by plugs of glass-wool. The result of the 
experiment was that about 200 cub. centims. of gas were collected. After sparking 
with oxygen in presence of caustic soda, the volume was reduced to 3 cub. centims. 
of a gas which appeared to be argon. 



mdccoxcv. — a. 2 \ 



C 243 ] 

VII. On the Spectra of Argon. 
By William Cuookes, F.R.S., d-c. 

Received January 2t>, — Read January 31, 1895. 

[Plate 3.] 

Through the kindness of Lord Bayleigh and Professor Ramsay I have been enabled 
to examine the spectrum of this gas in a very accurate spectroscope, and also to take 
photographs of its spectra in a spectrograph fitted with a complete quartz train. 
The results are both interesting and important, and entirely corroborate the con- 
clusions arrived at by the discoverers of argon. 

The results of my examination are given in a table of wave-lengths, which follows, 
and on a map of the lines accurately drawn to scale, accompanying this paper (Plate 3). 
The map is 40 feet long, and the probable error of position of any line on it is not 
greater than 1 millimetre. 

Argon resembles nitrogen in that it gives two distinct spectra according to the 
strength of the induction current employed. But while the two spectra of nitrogen 
are different in character, one showing fluted bands and the other sharp lines, both 
the argon spectra consist of sharp lines. It is, however, very difficult to get argon 
so free from nitrogen that it will not show the nitrogen flutings superposed on its own 
special system of lines. I have used argon prepared by Lord Bayleigh, Professor 
Bamsay, and myself, and, however free it was supposed to be from nitrogen, I 
could always at first detect the nitrogen bands in its spectrum. These, however, 
disappear when the induction spark is passed through the tube for some time, 
varying from a few minutes to a few hours. The vacuum tubes best adapted for 
showing the spectra are of the ordinary Plucker form having a capillary tube in the 
middle. For photographing the higher rays which are cut off by glass I have used a 
similar tube, " end on," having a quartz window at one end. I have also used a 
Plucker tube made entirely of quartz worked before the oxy- hydrogen blow-pipe. I 
have not yet succeeded in melting platinum or iridio-platinum wire terminals into 
the quartz, as they melt too easily, but a very good spectrum is obtained by coating 
the bulbs outside with tin foil, connected with the terminals of the induction coil. 

The pressure of argon giving the greatest luminosity and most brilliant spectrum 
is 3 millims. At this point the colour of the discharge is an orange-red, and 
the spectrum is rich in red rays, two being especially prominent at wave-lengths 696*56 
and 705*64. On passing the current the traces of nitrogen bands disappear, and 
the argon spectrum is seen in a state of purity. At this pressure the platinum from 
the poles spatters over the glass of the bulbs, owing to what I have called '* electrical 

MDCCCXCV.— A. 2 I 2 27.6.95. 



244 MR. W. CROOKBS ON THE SPECTRA OF ARGON. 

evaporation,"* and I think the residual nitrogen is occluded by the finely-divided 
metal. Similar occlusions are frequently noticed by those who work much with 
vacuum-tubes. 

If the pressure is further reduced, and a Leyden jar intercalated in the circuit, the 
colour of the luminous discharge changes from red to a rich steel blue, and the 
spectrum shows an almost entirely different set of lines. The two spectra, called for 
brevity red and blue, are shown on the large map, the upper spectrum being that of 
" blue" argon, and the lower one that of " red " argon. It is not easy to obtain the 
blue colour and spectrum entirely free from the red. The red is easily got by using 
a. large coilt actuated with a current of 3 amperes and 6 volts. There is then no 
tendency for it to turn blue. The blue colour may be obtained with the same coil by 
actuating it with a current of 3 "8 4 amperes and 11 volts, intercalating a jar of 
50 square inches surface ; the make-and- break must be screwed up so as to vibrate 
as rapidly as possible. With the small coil a very good blue colour can be obtained by 
using three Grove's cells and a Leyden jar of 120 square inches surface, and a very 
rapid make-and-break. It appears that an electromotive force of 27,600 volts is 
required to bring out the red, and a higher E.M.F. and a very hot spark for the blue. 
It is possible so to adjust the pressure of gas in the tube that a very slight alteration 
of the strength of the current will cause the colour to change from red to blue, and 
vice versa. 1 have occasionally had an argon tube in so sensitive a state, that 
with the commutator turned one way the colour was red, and the other way 
blue. Induction coils actuated by a continuous current are never symmetrical as 
regards the polarity of the induced current, and any little irregularity in the metallic 
terminals of the vacuum-tube also acts as a valve. The red glow is produced by the 
positive spark and the blue by the negative spark. 

I have taken photographs of the two spectra of argon partly superposed. In this 
way their dissimilarity is readily seen.^ In the spectrum of the blue glow I have 
counted 119 lines, and in that of the red glow 80 lines, making 199 in all. Of these 
26 appear to be common to both spectra. 

I have said that the residual nitrogen is removed by sparking the tube for some 
time when platinum terminals are sealed in. This is not the only way of purifying 
the argon. By the kindness of Professor Ramsav, I was allowed to take some vacuum 
tubes to his laboratory and there exhaust and fill them with some of his purest argon. 
On this occasion I simultaneously filled, exhausted, and sealed off two Pliicker tubes, 
one having platinum and the other aluminium terminals. On testing the gas 
immediately after they were sealed off, each tube showed the argon spectrum, con- 

* 'Roy. Soc. Proc.,' vol. 50, p. 88, June, 1891. 

t The coil used has about 60 miles of secondary wire, and when fully charged gives a torrent of sparks 
24 inches long. The smaller coil gives six-inch sparks when worked with six half-pint Grove's cells. 

J Photographs of the different spectra of argon, and other gaseous spectm for comparison, were 
projected on the screen. 



MR. W. CROOKES ON THE SPECTRA OF ARGON. 245 

taminated by a trace of nitrogen bands. The next day the tube with platinum 
terminals was unchanged, but that having aluminium terminals showed the pure spec- 
trum of argon, the faint nitrogen bands having entirely disappeared during the night. 
After an hoar's current and a few days' rest the tube with platinum terminals likewise 
gave a pure argon spectrum. When a mixture of argon with a very little nitrogen is 
submitted to the induced current in a tube made of fused and blown quartz, with- 
out inside metallic terminals, the nitrogen bands do not disappear from the argon 
spectrum, but the spectra of argon and nitrogen continue to be seen simultaneously. 

A vacuum-tube was filled with argon and kept on the pump while observations 
were made on the spectrum of the gas as exhaustion proceeded. The large coil was 
used with a current of 8 '84 amperes and 11 volts, no jar being interposed. At a 
pressure of 3 millions, the spectrum was that of the pure red glow. This persisted as 
the exhaustion rose, until, at a pressure of about half a millimetre, flashes of blue 
light made their appearance. At a quarter of a millimetre the colour of the ignited 
gas was pure blue, and the spectrum showed no trace of the red glow. 

A striking instance of a change of spectrum from nitrogen to argon was shown in 
a tube filled with argon kindly sent me by Lord Rayleigh. It had been prepared 
from the atmosphere by sparking, and it was considered to contain about 3 per cent, 
of nitrogen. This argon was passed into an exhausted tube and then rarefied to a 
pressure of 75 millims. and kept on the pump. At this pressure the nitrogen con- 
ducted all the induction current, the spectrum showing nothing but the nitrogen 
bands. The pump was slowly kept going and spectrum observations were con- 
tinuously taken. When the pressure fell to about 3 millims. a change came over 
the spectrum, the nitix)gen bands disappeared, and the spectrum of argon took its 
place, the only contamination being a little aqueous vapour, due to my not having 
sufficiently dried the gas. I took photographs of the spectrum given by this tube in 
the two stages, one showing the pure nitrogen bands and the other the argon lines, 
each being compared with the spectrum of argon prepared by Professor Ramsay. 
Observations have shown that the spectra given by argon, obtained by the sparking 
method of Lord Rayleigh and by the magnesium method of Professor Ramsay from 
the atmosphere, are identical. 

It was of interest to see how little argon could be detected in admixture with 
nitrogen by combined pumping and passage of the current. Some argon prepared 
by myself,* having 60 to 70 per cent, of nitrogen with it, was put into a small tube 
furnished with large platinum terminals. Exhaustion was carried to 3 millims., and 

* When a current of 65 volts and 15 amperes, alternating 130 times a second, is passed through the 
primary of my large coil, an arching flame, consisting of burning nitrogen, issues from each of the 
secondary poles, meeting in the middle. When once started, the poles can be drawn asunder till the 
flame bridges across 212 millims. When the terminals are more than 46 millims. apart, the flame will 
not strike across. By enclosing this flame in a reservoir over alkaline water and feeding it with air and 
oxygen I can burn up a litre of air an hour. 



246 MR. W. CROOKES ON THE SPECTRA OF ARGON. 

the tube was then sealed off. The spark from the large coil, actuated with a current 
of 3*84 amperes and 11 volts, was then put on, and the spectrum examined con- 
tinuously. At first it showed only the nitrogen bands ; in about half an hour the 
nitrogen began to fade and the argon lines appeared, and in a few minutes later the 
tube was just short of non-conducting. The colour of the gas was rich steel blue, 
and the spectrum was that of the blue argon glow. Here the small diameter of 
the bulbs of the tube and the large platinum wires facilitated much spattering 
or -' electrical evaporation " of the platinum ; the pressure also was the one most 
suitable lor that phenomenon. To this I attribute the rapid occlusion of the 
residual nitrogen. 

An experiment was now made to see if the small quantity of argon normally present 
in the atmosphere could be detected without previous concentration. Nitrogen was 
prepared from the atmosphere by burning phosphorus, and was purified in the usual 
manner. This gas, well dried over phosphoric anhydride, was passed into a vacuum 
tube, the air washed out by two fillings and exhaustions, and the tube was finally 
sealed off at a pressure of 52 millims. It was used for photographing the band 
spectrum of nitrogen on several occasions, and altogether it was exposed to the 
induction current from the large coil for eight hours before any change was noticed. 
The last time I used it for photographing the nitrogen spectrum difficulty was 
experienced in getting the spark to pass, so I increased the current and intercalated a 
small jar. The colour immediately changed from the reddish-yellow of nitrogen to the 
blue of argon, and on applying the spectroscope the lines of argon shone out with 
scarcely any admixture of nitrogen bands.. With great difficulty, and by employing 
a very small jar, I was able to take one photograph of this changed spectrum and 
compare it with the spectrum of argon from Professor Ramsay, both being taken on 
the same plate, but the tube soon became non-conducting, and I could not then force 
a spark through except by employing a dangerously large current. Whenever a 
Hash passed it was of a deep blue colour. Assuming that the atmosphere contains 
1 per cent, of argon, the 3 millims. of nitrogen originally in the tube would contain 
0'03 millim. of argon. After the nitrogen had been occluded by the spattered 
platinum this pressure of argon would be near the point of non-conduction. 

In all cases, when argon has been obtained in this manner, the spectrum has been 
that of the blue-glowing gas. Very little of the red rays can be seen. The change 
from red to blue is chiefly dependent on the strength and heat of the spark ; partly 
also on the degree of exhaustion. Nitrogen, when present, conducts the current 
easiest. As the exhaustion increases and the conductivity of the nitrogen diminishes, 
that of the red-glowing ai'gon rises, until, at a pressure of about 3 millims., its 
conductivity is at the greatest, and the luminosity is best. Beyond that point the 
conductivity of the red form seems to get less, and that of the blue form to increase, 
till the vacuum approaches a fraction of a millimetre, when further pumping soon 
renders it non-conducting. It is not improbable, and I understand that independent 



MR. W. CROOKES ON THE SPECTRA OF ARGON. 247 

observations have already led both the discoverers to the same conclusion, that the 
gas argon is not a simple body, but is a mixture of at least two elements, one of 
which glows red and the other blue, each having its distinctive spectrum. The 
theory that it is a simple body has, however, support from the analogy of other gases. 
Thus, nitrogen has two distinct spectra, one or the other being produced by varying 
the pressure and intensity of the spark. I have made vacuum tubes containing 
rarefied nitrogen, which show either the fluted band or the sharp line spectrum by 
simply turning the screw of the make-and-break, exactly as the two spectra of argon 
can be changed from one to the other. 

The disappearance of the red glow and the appearance of the blue glow in argon as 
the exhaustion increases also resembles the disappearance of the red line of hydrogen 
when exhaustion is raised to a high point. Plucker, who was the first to observe 
this occurrence, says :* " When Ruhmkorff's small induction coil was discharged 
through a spectral tube enclosing hydrogen, which was gradually rarefied to the 
highest tenuity to be reached by means of Geissler's exhauster, finally the beautiful 
red colour of the ignited gas became fainter, and passed gradually into an undetermined 
violet. When analysed by the prism, Ha (the red, C, line) disappeared, while H/3 
(the green, F, line), though fainter, remained well defined. Accordingly, light of a 
greater length of wave was the first extinguished." 

The line spectrum of nitrogen is not nearly so striking in brilliancy, number, 
or sharpness of lines as are those of argon, and careful scrutiny fails to shoAV 
more than one or two apparent coincidences between lines in the two spectra. 
Between the spectra of argon and the band spectrum of nitrogen there are two or 
three close approximations of lines, but a projection on the screen of a magnified 
image of the two spectra partly superposed shows that two at least of these are not 
real coincidences. 

I have looked for indications of lines in the argon spectra corresponding to the 
corona line at 531'7, the aurora line at 557*1, and the helium line at 587*5, but have 
failed to detect any line of argon sufficiently near these positions to fall within the 
limits of experimental error. 

I have found no other spectrum-giving gas or vapour yield spectra at all like those 
of argon, and the apparent coincidences in some of the lines, which on one or two 
occasions are noticed, have been very few, and would probably disappear on using a 
higher dispersion. Having once obtained a tube of argon giving the pure spectra, I 
can make no alteration in it, except that which takes place on varying the spark or 
increasing the exhaustion, when the two spectra change from one to the other. As 
far, therefore, as spectrum work can decide, the verdict must be that Lord Rayleigh 
and Professor Ramsay have added one, if not two, members to the family of 
elementary bodies. 

* " On the Spectra of Ignited Gases and Vapours." By Drs. Pi.uckeb and Hittorf, ' Phil. Trans.,' 
Part I., vol. 155. p. 21. 



248 



MR, W. CROOKES ON THE SPECTRA OF ARGON, 



William Grookes. January 24, 1895. 
The Two Spectra of Argon. 



Bine. 


Red. - 




Wave-length. 


Intensity. 


Wave-length. 


Intensity. 








764-6 


2 








750-6 


4 








737-7 


3 








726-3 


2 




_ 




705-64 


10 








696-56 


9 








684-2 


2 








675-4 


6 








666-4 


6 




662-8 


4 


640-7 
637-7 
630-2 
628-1 


9 
2 

4 
2 




623-2 


4 


621-0 


6 




617-3 


6 


6173 

614-3 


6 
2 


Coincident. 


612-0 


6 


609-9 
605-G 
604-5 


4 
2 
3 




603-8 


8 


603-8 
5935 


8 
1 


Coincident. 


592-6 


4 


592-6 

590-9 

588-7 

585-8 

583-4 

580-3 

577-1 

574-6 

568-3 

565-1 

561-0 

556-7 

555-7 

552-0 

5501 

549-65 

545-6 

544-4 

542-1 

525-8 

522-2 

518-58 

516-5 


4 
6 
6 
4 
2 
1 
2 
6 
2 
9 
9 
2 

10 

] 
2 
8 
6 
2 
4 
6 
7 
10 
9 


Coincident, 



MR, W. CROOKES ON THE SPECTRA OF ARGON. 



249 



The Two Spectra of Argon — (continued). 



Blue. 


Red. 




"Wave-length. 


Intensity. 


Wave-length. 


Intensity. 


514-0 


10 






506-5 


10 


506-5 


4 


Coincident. 


501-2 


2 


501-2 


4 


Coincident. 


500-7 


9 








496-55 


9 


496-55 


4 


Coincident. 


4938 


10 


493-8 


2 


Coincident. 


487-9 


10 


487-9 


4 


Coincident. 


484-75 


1 








480-50 


7 








476-30 


1 








473-45 


6 








47266 


2 


470-12 


8 




465-65 


5 


462-95 


5 




460-80 


8 


459-45 


2 




458-69 


6 








457-95 


6 








454-35 


7 


451-40 


2 




450-95 


8 


450-95 


9 


Coincident. 


447-83 


6 








442-65 


10 








442-25 


10 








439-95 


10 








437-65 


9 








436-90 


9 








434-85 


10 


434-50 


5 




43335 


9 


433-35 

430-05 


9 

9 


Coincident. 


429-90 


9 








427-70 


3 








427 20 


7 


427-20 


8 


Coincident. 


426-60 


6 


426-60 


4 


Coincident. 


4-25-95 


8 


425-95 


9 


Coincident. 


425-15 


2 


425-15 


3 


Coincident. 


422-85 


6 








420-10 


10 


420-10 • 


10 


Coincident. 


419-80 


9 


419-80 


9 


Coincident. 


419-15 


9 


419T5 


9 


Coincident. 


418-30 


8 


418-30 


8 


Coincident. 


416-45 


8 


416-45 


4 


Coincident. 


415-95 


10 


415-95 
415-65 


10 
6 


Coincident. 


413T5 


3 








410-50 


8 








407-25 


8 








404-40 


8 


404-40 


9 


Coincident. 


403-30 


1 








401-30 


8 








397-85 


1 








396-78 


3 









MDCCCXCV. 



2 K 



250 



MR. W. CROOKES ON THE SPECTRA OF ARGON. 



The Two Spectra of Argon — (continued). 



Blue. 


Red. 


Coincident. 


Wave-length. 


Intensity. 


Wave-length. 


Intensity. 


394-85 


9 . 


394-85 


10 


394-35 


3 








393-18 


3 








392-85 


9 








392-75 


3 








391-50 


1 


390-45 


8 




389-20 


5 








387-55 


2 








387-18 


2 








386-85 


8 








385-15 


10 








384-55 


1 








383-55 


2 


383-55 


3 


Coincident. 


382-75 


2 








380-95 


4 








380-35 


1 








379-95 


1 








378-08 


9 


377-15 


1 




37705 


2 








376-60 


8 








373-85 


3 








372-98 


10 








371-80 


4 


363-25 


2 




363-17 


1 


362-37 
362-28 


1 
1 




361-75 


2 








360-50 


3 


360-50 


5 


Coincident. 


358-70 


10 








358-03 


- 9 








357-50 


9 








356-65 


2 


356-65 


4 


Coincident. 


356-40 


2 


356-28 


1 




356-00 


2 








355-82 


7 








355-45 


4 


• 355-45 


6 


Coincident. 


354-75 


4 








354-45 


7 








353-43 


4 








352-05 


3 








351-92 


4 








351-35 


6 








350-88 


4 








349-00 


10 








347-57 


7 








345-35 


1 








338-80 


1 








309-27 


5 








308-48 


4 








306-47 


2 









MR. W. CROOKES ON THE SPECTRA OP ARGON. 



251 



The Two Spectra of Argon — -(continued). 



Blue. 


Red. 




Wave-length. 


Intensity. 


Wave-length. 


Intensity. 


304-27 
299-S2 
297-86 
294-27 
292-96 
283-02 
279-44 
273-45 
270-72 
269-30 
266-12 
265-26 
262-95 
257T2 
250-07 
248-49 
243-85 
224-66 


3 
1 

1 

2 

1 

1 

2 

2 

0-5 

1 

2 

3 

1 

2 

1 

1 

2 

3 







119 lines in the " Blue " Spectrum. 
SO lines in the "Red" Spectrum. 

199 total lines. 
26 lines common to the two spectra. 



Note. — In the spectroscope the lines of argon appear almost equally fine, but of 
very different intensities. This difference of brightness is represented in the 
accompanying map by a variation in the thickness of the lines, faint lines being 
made narrow and strongly luminous lines being widened. In some cases two or 
three strong lines are too close together to enable their intensities to be represented 
in this way without overlapping. This is the case with lines 442*65 and 442-25, 
with lines 42010, 419-80, and 419-15, and with lines 415-95 and 41565. In these 
cases I have indicated the centres of the strong lines by short projecting lines 
beneath. 



2 K 2 



Crool-es. 



Phil. Trans., 1895, A, Plate 3. 



THE SPECTRA OF ARGON. 



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[ 253 ] 



VIII. The Liquefaction and Solidification of Argon. 

By Dr. K. Olszewski. Professor of Chemistry in the University of Cracow. 

Communicated by Professor William Ramsay, F.R.S. 

Received January 28, — Read January 31, 1895. 



Havixg been furnished, by Professor Ramsay's kindness, with a sample of the new 
gas, argon, I have carried out experiments on its behaviour at low temperatures and 
at high pressures, in order to contribute, at least in part, to the knowledge of the 
pi'operties of this interesting body. 

The argon sent by Professor Ramsay amounted to 300 cub. centims. It was 
contained in a hermetically-sealed glass bulb, so constructed that it could easily be 
transferred, with no appreciable loss, into the carefully-dried and vacuous apparatus 
in which the proposed experiments were to be performed. The argon with which I 
was supplied had, according to Professor Ramsay's statement, been dried with phos- 
phoric anhydride ; its density was 19 "9 (H = 1) ; and he thought that at the outside 
it might contain 1 to 2 per cent, of nitrogen, although it showed no nitrogen spectrum 
when examined in a Plucker's tube. 

Four series of experiments in all were carried out, two with the object of deter- 
mining the critical temperature and pressure of argon, as well as of measuring its 
vapour pressure at several other low temperatures, while two other series served to 
determine its boiling- and freezing-points under atmospheric pressure, as well as its 
density at its boiling-point. 

A detailed description of these experiments will be given in another place ; I shall 
here give only a short description of the manner in which they were made. 

For the first two experiments I made use of a Cailletet's apparatus. Its metallic 
manometer had been previously compared with the readings of a mercury manometer. 
As cooling agent I used liquid ethylene, boiling under diminished pressure. The 
glass tube of Cailletet's apparatus was so arranged that the portion immersed in 
the liquid ethylene had comparatively thin walls (not exceeding 1 millim.), so as to 
equalize the external and internal temperature as quickly as possible. 

In both the other experiments the argon was contained in a burette, closed at both 

27.6.95 



254 



PROFESSOR K. OLSZEWSKI ON THE 



ends with glass stop-cocks. By connecting the lower end of the burette with a 
mercury reservoir, the argon was transferred into a narrow doubly bent glass tube 
connected with the upper end of the burette, and in which the argon was liquefied, and 




its volume in the liquid state measured. In these two series of experiments liquid 
oxygen, boiling under atmospheric or under diminished pressure, was employed as a 
cooling agent. I made use of a hydrogen thermometer in all these experiments to 
measure low temperatures. 



Determination of the Critical Constants of Argon. 

As soon as the temperature of the liquid ethylene had been lowered to — 128°"G, 
the argon easily condensed to a colourless liquid under a pressure of 38 atmospheres. 
On slowly raising the temperature of the ethylene, the meniscus of the liquid argon 
became less and less distinct, and finally vanished at the following temperatures and 
corresponding pressures : — 



LIQUEFACTION AND SOLIDIFICATION OF ARGON. 



255 



Experiment. 


Temperature. 


Pressure. 




o 


atmos. 


1 - 


- 121-2 


50-6 


2 


- 121-6 


50-6 


3 


- - 120-5 


50-6 


4 


- 121-3 


50-6 


5 


- 121-4* 


50-6 


6 


- 119-S 


50-6 


7 


- 1213 


50-6 



In all seven determinations the critical pressure was found to be 50*6 atmospheres ; 
but determinations of the critical temperature show slight differences. In experiments 
Nos. 3 and 6 less liquid argon was present in the tube than in the other five ; in 
these the volume of liquid exceeded the volume of gas. 

In determining the vapour pressures of argon, a tabular record of which is given 
below, I noticed slight differences of pressure according as I produced more or less of 
the liquid at the same temperature. This proved that the sample of argon contained 
an inconsiderable admixture of another gas, more difficult to liquefy ; it is doubtless 
the trace of nitrogen previously referred to. The mean of the seven estimations of 
the critical temperature is — 121°, and this may be taken as the critical temperature 
of argon. 

At lower temperatures the following vapour-pressures were recorded : — 



Experiment. 


Temperature. 


Pressure. 


Experiment. 


Temperature. 


Pressure. 







atmos. 




o 


atmos. 


8 


-128-6 


38-0 


13 


-134-4 


29-8 


9 


-129-6 


35-8 


14 


-135-1 


29-0 


10 


-129-4 


35-8 


15 


-136-2 


27-3 


11 


-129-3 


35-8 


16 


-1383 


25-3 


12 


-129-6 


35-8 


17 


-139-1 


23-7 



In Experiments Nos. 9, 10, and 17 the quantity of liquefied argon was very small, 
for it filled the tube only to a height of 3 to 5 millims., and in the other experiments 
the column of liquid argon was 20 millims. or more. 



Determination of the Boiling- and Freezing-Points. 

Two hundred cub. centims. of liquid oxygen, prepared in my large apparatus,* was 
poured into a glass vessel with quadruple walls, so as to isolate the liquid from 



* ' Bulletin International de l'Academie de Cracovie,' June, 1890 ; also Wiedemann's ' Beiblatter,' 
vol. 15, p. 29. 



256 PROFESSOR K. OLSZEWSKI ON THE 

external heat. After the liquid oxygen had been thus poured under atmospheric 
pressure, a great part of it evaporated, but there still remained about 70 cub. centims., 
boiling under atmospheric pressure. A calibrated tube, intended to receive the argon 
to be liquefied, and the hydrogen thermometer were immersed in the boiling oxygen. 
At this temperature ( — 182°'7 # ) on admitting argon, no appearance of liquefaction 
could be noticed, even when compressed by increasing the atmospheric pressure by a 
quarter. This shows that its boiling-point lies below that of oxygen. But on 
diminishing the temperature of the liquid oxygen below — 187°, the liquefaction of 
the argon became manifest. When liquefaction had taken place, I carefully equalised 
the pressure of the argon with that of the atmosphere, and regulated the temperature, 
so that the state of balance was maintained for a long time. This process gives the 
boiling-point of argon under atmospheric pressure. Four experiments gave the 
numbers: — 186°7, - 186°-8, — 187 o> 0, and — 187 3 '3. The mean is — 186°-9, 
which I consider to be the boiling-point under atmospheric pressure (740"5 millims.). 

The quantity of argon used for these experiments, reduced to normal temperature 
and pressure, was 99 - 5 cub. centims. ; the quantity of liquid corresponding to that 
volume of gas was approximately 0"114 cub. centim. Hence the density of argon at 
its boiling-point maybe taken as approximately 1*5. Two other determinations of 
the density of liquid argon, for which I employed still smaller quantities of the gas, 
yielded rather smaller numbers. Owing to the small amount of argon used for these 
experiments, the numbers given cannot lay claim to great exactness ; yet they prove 
that the density of liquid argon at its boiling-point ( — 187°) is much higher than 
that of oxygen, which I have found, under similar conditions, to be 1"124. 

By lowering the temperature of the oxygen to — 191° by slow exhaustion, the 
argon froze to a crystalline mass, resembling ice ; on further lowering temperature it 
became white and opaque. When the temperature was raised it melted ; four obser- 
vations which I made to determine its melting-point gave the numbers: — 189°'0, 
— 190°-6, — 189°-6, and — l89°-4. The mean of these numbers is — 189°-6 ; and 
this may be accepted as the melting-point of argon. 

In the following table I have given a comparison of physical constants, in which 
those of argon are compared with those of other so-called permanent gases. The data 
are from my previous work on the subject. 



* I have re-determined the boiling-point of oxygen, using large quantities of oxygen, and a hydrogen 
thermometer of much larger dimensions than previously. The registered temperature is l° - 3 lower than 
that which I previously recorded. 



LIQUEFACTION AND SOLIDIFICATION OF ARGON. 



257 



! 














Density 




Name. 


tempera- 
ture. 


Critical 
pressure. 


Boiling- 
point. 


Freezing- 
point. 


Freezing 
pressure. 


Density 
of gas. 


of liquid 

at boiling 

point. 


Colour of 
liquid. 






Atmos. 


o 


o 


millims. 








Hydrogen (H 2 ) . . 


/ Below. 

1 -220-0 


j 20-0 


? 


? 


? 


10 


p 


Colourless 


Nitrogen (N,) . . 


-146-0 


35-0 


-194-4 


-214-0 


60 


14-0 


0-885 




Carbonic oxide (CO) 


-1395 


35-5 


-190-0 


-207-0 


100 


14 


r 


)> 


Argon (A x ) . . . 


-121-0 


50-6 


-187-0 


-189-6 


? 


19-9 


/ About 
I 1-5 


} » 


Oxygen (0.-,) . . . 


-118-8 


50-8 


-182-7 


? 


? 


16-0 


1-124 


Bluish 


Nitric oxide (NO) . 


- 93-5 


71-2 


-153-6 


-167-0 


138 


150 


P 


Colourless 


Methane (CHJ . . 


- 81-8 


54-9 


-164-0 


-185-8 


80 


8-0 


0-415 


}? 



As can be seen from the foregoing table, argon belongs to the so-called " permanent " 
gases, and, as regards difficulty in liquefying it, it occupies the fourth place, viz., 
between carbon monoxide and oxygen. Its behaviour on liquefaction places it nearest 
to oxygen, but it differs entirely from oxygen in being solidifiable ; as is well known, 
oxygen has not yet been made to assume a solid state 

The high density of argon rendered it probable that its liquefaction would take 
place at a higher temperature than that at which oxygen liquefies. Its unexpectedly 
low critical temperature and boiling-point seem to have some relation to its simple 
molecular constitution. 



Note ox a Comparison of the Vapour-Pressures oe Argon with those of 

other Substances. 

By "William Ramsay and Sydney Young. 



Received February 7, 1895. 

The vapour-pressures of a considerable number of substances have been determined 
from low temperatures to the critical points, but as the critical pressure of argon is 
somewhat high, the boiling-points of very few are available for comparison through the 
whole range of equal pressures. 

The critical pressure of benzene is so slightly below that of argon that the extra- 
polation of the vapour-pressure curve through the few degrees necessary to afford a 
comparison at the critical pressure of the new element is justifiable. 

The other two substances chosen are ethyl alcohol and oxygen ; the second is 
interesting, as its vapour-pressures, like those of argon, have been determined 
by Professor Olszewski. 

In the following table the boiling-points — on the absolute scale — of argon, benzene, 

MDCCCXCV. — A. 2 L 



258 



PROFESSOR K. OLSZEWSKI ON THE 



ethyl alcohol, and oxygen, are given at the pressures at which observations have been 
made with the first of these substances. 



BoiLTNG-Points on Absolute Scale. 



Pressure in 
millims. 


Argon. 


Benzene. 


Ethvl alcohol. 


Oxygen. 


740-5 


86-1 


352-5 


350-65 


90-1 


18010 


133-9 


507-8 


462-6 


136-1 


19230 


134-7 


512-5 


465-8 


137-4 


20750 


136-8 


518-0 


469-6 


139-0 


22040 


1379 


522-3 


472-7 


140-2 


22650 


138-6 


524-3 


474-0 


141-4 


27210 


143-5 


5383 


483-7 


145-0 


28880 


144-4 


543-0 


487-0 


146-5 


' 38460 


1520 


565-9 


503-1 


1537 



The ratios of the absolute temperatures of argon to each of the other substances 
were calculated and plotted against the centigrade temperatures of the latter. 
Straight lines were then drawn to pass as well as possible through the points, and the 
following formulae for the ratios were obtained :— 



Argon 



-5 — - — R'= - 2351 + '0001155 t (t = temperature centigrade of benzene). 

Argon 
Etl I a] , i i R'= "2164 + '0003765 t (t = temperature centigrade of ethyl alcohol). 

Argon 

H'= '9518+ 000522 (Z+190) (t = temperature centigrade of oxygen). 



Oxygen 



The ratios calculated from the boiling-points and those given by the above formulae 
are compared in the following table : — 



Pressure 
in 


Ratios. 


Argon/E 


enzene. 


Argon/Alcoliol. 


Argon/Oxygen. 


millims. 










From 


From 


From 


From 


From 


From 




boiling-points. 


formula. 


boiling-points. 


formula. 


boiling-points. 


formula. 


740-5 


•2443 


•2443 


■2455 -2456 


•9556 


•9555 


18010 


•2637 


•2622 


•2894 


•2878 


■9838 


•9795 


19230 


•2628 


■2628 


•2892 


•2890 


•9804 


•9802 


20750 


•2641 


•2634 


•2913 


•2904 


•9842 


•9810 


22040 


•2640 


•2639 


•2917 


■2916 


•9836 


•9817 


22650 


■2644 


•2641 


•2924 


•2921 


•9802 


. -9823 


27210 


•2666 


•2657 


•2967 


■2957 


■9896 


•9842 


28880 


•2659 


•2663 


•2965 


•2970 


■9857 


•9850 


38460 


•2686 


•2689 


•3021 


•3030 


•9889 


•9887 



LIQUEFACTION AND SOLIDIFICATION OF ARGON. 



259 



Assuming the boiling-points of benzene, alcohol, and oxygen to be correct, those of 
argon could be calculated from them by multiplying the absolute temperatures of each 
substance by the corresponding ratio at each pressure. 

The observed and re-calculated absolute temperatures of argon and the differences 
are given below : — 



Pressure 

in 
miUims. 




Boiling-poir 


ts (absolute) of 


argon. 






Observed. 


From benzene. 


A. 


From alcohol. 


A - 


From oxygen. 


A. 


740-5 


86-1 


86-1 





86-1 





86-1 


o 


18010 


133-9 


1331 


-0-8 


133-1 


-0-8 


1333 


-0-6 


19230 


134-7 


134-7 





134-6 


-o-i 


134-7 





20750 


136-8 


136-4 


-0-4 


1364 


-0-4 


136-4 


-0-4 


22040 


137-9 


137-8 


-o-i 


137-8 


-o-i 


1376 


-0-3 


22650 


138-6 


138-5 


-o-i 


138-5 


-o-i 


138-9 


+ 0-3 


27210 


143-5 


1430 


-0-5 


143-0 


-0-5 


142-7 


-0-8 


28880 


144-4 


144-6 


+ 0-2 


144-6 


+ 0-2 


144-3 


-o-i 


38460 


152-0 


152-2 


+ 0-2 


152-4 


+ 0-4 


152-0 






The comparison would, of course, be more valuable if there were some observations 
between 740 and 18,000 millims., but, so far as it goes, it will be seen that there is 
a very fair agreement between the observed temperatures and those calculated from 
the smoothed ratios. 

It is hardly likely, though not impossible, that so good an agreement would be 
obtained with a mixture or an impure substance. It is, at any rate, certain that a 
distinct want of agreement would have shown that the argon was not a definite, pure 
substance, and the results may be taken as affording additional confirmation of the 
conclusion that argon is a definite, hitherto unknown constituent of the atmosphere, 
and that it has been isolated in a state very closely approaching to purity. 



2l2 



[ 261 ] 



IX. The Latent Heat of Evaporation of Water. 

By E. H. Griffiths, M.A., Sidney Sussex College, Cambridge. 

Communicated by E.. T. Glazebrook, F.R.S. 

Received December 28, 1894, — Read January 17, 1895. 

[Plates 4-6.] 
Contents. 

Section. Page. 

I. Introductory note 261 

II. Historical 263 

III. Description of the method 270 

IV. Method of maintaining the walls of the surrounding chamber at a constant 

temperature 274 

V. Description of the calorimeter and its contents 276 

VI. The determination of 2g. . 282 

VII. The heat supplied by the stirring 290 

Vffl. „ „ „ current 294 

IX. Results of experiments in which the evaporation was promoted by the passage of 

a gas 298 

X. The method finally adopted 303 

XL Discussion of the results, together with a note by Dr. Jolt, F.R.S 316 

XII. The density of water-vapour 323 

Details of Experiments. 
Appendix. 

I. The stirring supply 327 

II. The capacity for heat of the calorimeter and the specific heat of the oil 333 

III. The resistance of the coil 338 

Plates. 
Plate. 

4. The steel chamber and regulating apparatus. 

5. The calorimeter. 

6. The gas circuit, the electrical circuit, and the differential thermometers. 

Section I.— Introductory Note. 

It is possible that I have in succeeding pages, when describing apparatus and 
methods of observation, entered unnecessarily into matters of detail. In defence, 

1.7.95. 



262 MR. E. H. GRIFFITHS ON THE LATENT 

I would urge that the accuracy of determinations of physical constants depends on 
the amount of attention devoted to apparently trivial matters, and that in the 
absence of full information, it is impossible to rightly estimate the value of the 
results. Corrections are often rendered necessary by subsequent re-determinations 
of the constants involved, and the application of such corrections is only possible 
when the writer has given his data in full. Much valuable experimental work has 
with lapse of time become useless, owing to the author's natural reluctance to over- 
crowd his communication with details which m^y at the time very possibly appear 
both unnecessary and trivial. 

Although the experiments described in this paper were not commenced until 
the Summer of last year (1894), the preparation of the apparatus and the 
standardisation of the instruments has engaged my attention for a considerable 
time. Nearly the whole of the Spring and Summer of 1893 were expended in 
fruitless efforts to render the calorimeter and its connections absolutely air-tight, and 
I found it impossible to secure perfection in this respect until in the Autumn of that 
year I succeeded in obtaining an alloy, by means of which I was able to unite glass 
and metal tubes in a satisfactory manner. The calorimeter and connections had then 
to be practically reconstructed and some improvements added, which experience had 
shown to be desirable. 

My original intention was to conclude my investigations into the latent heat of 
evaporation of water over the range 10° to 60° C before publishing my results, and, 
had it not been for two misfortunes, I think that I should have now completed the 
necessary experiments. An accident to the apparatus early in September involved 
a loss of about ten days, and also compelled a redetermination of the capacity for 
heat of the calorimeter. A second mischance was a temporary break-down in my 
health, which compelled me to be absent from my laboratory for some days, and on 
resuming the work I was at first able to devote but little energy to it. During the 
University Term my time is not my own, and hence, when October 13 found the 
inquiry unfinished, I was compelled to relinquish all hopes of completing my original 
scheme until the Long Vacation of 1895 should again provide me with the necessary 
leisure. 

I feel, however, that all the experimental difficulties have been overcome, and I 
regard the work as completed at certain temperatures. I do not propose to repeat 
the observations at those temperatures, and therefore I see no necessity to defer the 
publication of the results for another twelve months. 

Again, the facts set forth in Section XL appear to me to so strengthen the 
conclusions to which my experiments have led me as to render any postponement 
unnecessary. 

I wish to express my sincere thanks to Mr. C. T. Heycock and Mr. F. H. Neville 
for many valuable suggestions, and also for their help with the experiments on 
certain critical occasions. 



HEAT OP EVAPORATION OP WATER. 



263 



During the summer of 1893 I was assisted by Mr. G. M. Clakk, B.A., and 

throughout 1894 by Mr. C. Green, Scholar of Sidney Sussex College, and I am glad 

to have this opportunity of acknowledging ray indebtedness to both those gentlemen. 

As frequent references have to be given to two former papers, I denote them as 

follows : — 

Paper J." " The Mechanical Equivalent of Heat," ' Phil. Trans.,' vol. 184 

(1893), A, pp. 361-504. 
Paper A." " The Influence of Temperature upon the Specific Heat of Aniline," 
' Phil. Mag.,' January, 1895. 

Section II. — Historical. 

The following is, I think, a fairly complete table of results published since the 

year 1843 : — 

Table I. 



Temperature. 


Observer. 


No. of 
experi- 
ments. 


Extreme 
values for L. 


Mean 
L.f 


Reference. 


0° 


Dieterici . . 


20 


595-52-598-84 


596-8 


' Wied. Ann ,' vol. 37, 1889 


- 2° to + 16" 


Regnault . . 


22 


. . 


, , 


'Memoir, de 1'Acad.,' vol. 21, 1847 


63°-88° 


)) • 


23 


. , 


. , 




99°-88 




44 


533-3-538-4 


536-67 




99°-81 


Favre and 

SlLBERMANN 


3 


532-59-541-77 


535 77 


' Ann. de Chimie,' vol. 37, 1853 


100° 


Andrews . . 


8 


530-8-543-4 


535-9 


' Chem. Soc. Joum.,' 1849 


100° 


Berthelot 


3 


535-2-537-2 


536-2 


' Comptes Rendus,' vol. 85, 1877 


100° 


SCHALL . . . 


No de 


tails given 


532-0 


' Ber. d. Ohem. Ges.,' vol. 17, 1884 


100°-16 


Hartog and 
Haeker* 


5 


523-61-525-87 


524-60 


'Manchester Phil. Soc. Proc.,' 
1893-4 


119°-194° 


Regnault . . 


73 






'Memoir, de l'Acad.,' vol. 21, 1847 



The values obtained by Winkelmann (' Wied. Ann.,' vol. 9, 1880) are not included 
in the above table, as they are not based on independent experiments, but deduced 
from the observations of Reg-nault. 

I do not propose to examine at length any of the above determinations except those 



* It is right to add that Messrs. Haetog and Harker state that these are the results of " Preliminary 
Experiments," and should not be regarded as giving their final conclusions. I do not, therefore, include 
their "work in my criticisms. 

t It must be remembered that all the above values of L (with the exception of Dieteeici's) defend 
upon some assumption as to the changes in the specific heat of water caused by changes in temperature, 
for they are either deduced from " the total heat of steam," or depend upon the observation of the rise 
or fall in temperature of a certain mass of water. Again, as the nature of the thermal unit adopted by 
the observer is, in some cases, doubtful, an uncertainty of an order of about 1 per cent, is thus 
introduced. 



264 MR. E. H. GRIFFITHS ON THE LATENT 

by Regnault and Dieterici, for none of the other observers appear to me to have 
devoted as much care and attention to the matter. In some cases, e.g., Andrews 
and Berthelot, we have records of only a few observations evidently undertaken not 
so much with the object of obtaining an accurate determination of the latent heat of 
evaporation of water, but rather for purposes of comparison with other liquids. In 
other cases there are not sufficient details as to the thermometry, the unit of heat 
adopted, &c, to render a close criticism of any profit. 

Again, Dieterici is the only observer who has made direct experiments at tempera- 
ture 0° C. Regnault's observations extended from 63° to nearly 200° C, and he also 
performed a number of experiments where the temperature of the vapour was between 
— 2° and + 16°, although this last group mast be regarded (and I think was regarded 
by Regnault himself) as of less value than his observations at higher temperatures. 

The method employed by Dieterici was in principle very similar to that adopted 
by me and described in subsequent pages.* 

The heat required for the evaporation was abstracted from' water at 0° and the 
amount of heat deduced from the quantity of ice formed. The advantages of such a 
method (upon which I shall more fully dwell when I describe my own work) are as 
follows : — 

(1.) No change of temperature takes place, thus all difficulties connected with the 
capacity for heat of the apparatus and its contents are avoided. 

(2.) The observer is almost entirely independent of thermometry — an advantage 
which, to my mind, it is almost impossible to overestimate. 

Dieterici' s experimental results, as stated in Table I. {supra), vary from 595 - 52 to 
598 - 84, but it should be noticed that both these extremes occur in his Table I. He 
afterwards made what he considered to be improvements in the apparatus, and the 
extreme values of his last 13 experiments (see his Tables II., III., IV.) are 59574 and 
597 "29. His mean result is 596'80, and I would particularly draw attention to his 
last two experiments, where he very greatly increased the rapidity of evaporation by 
suddenly opening the communication between his evaporating vessel and a condenser 
containing sulphuric acid in which the pressure was reduced as far as possible by 
means of a mercury pump. These two experiments give respectively 597*07 and 
596 "68. The agreement between the individual experiments throughout the whole 
series leaves little to be desired, and, if it were not for one doubt, I would without 
hesitation accept those results as conclusive ; but I am afraid, for the following 
reasons, that our knowledge is not yet sufficiently exact. 

The quantities of heat were deduced by measuring the mass of mercury expelled 
from the Bunsen calorimeter during the formation of ice. and the results, therefore, 

* My own experiments described in this paper were completed before the work of Dieterici came to 
my notice, and the close similarity between the general principles adopted by both of us is a matter of 
chance, not of design. Had I previously perused his paper, I should have been saved much time and 
mauy preliminary experiments. 



HEAT OF EVAPORATION OF WATER. 265 

depend entirely on the constant which gives the relation between the quantity of 
heat and the mass of expelled mercury. Dieterici in this matter shifts the respon- 
sibility on to other shoulders. His only reference to the subject is as follows : — 

" Diese sind gemessen in mittleren Calorien, also in deni hundertsten Theile 
derjenigen Warmemenge, welche ein Gramm Wasser von 0° auf 100° erwarmt, und 
zwar liegt der Berechnung der Mittelwerth der Beobachtungen von Bunsen, 
Schuller und Wartha und Velten,* zu Grunde dass einer mittleren Calorie 
15*44 mg. Hg. entsprechen."t 

Now, Bunsen by assuming his own value of this constant obtained 80 - 025 as the 
latent heat of fusion of ice, and the marked difference between this number and that 
obtained by Regnault (79 - 24), requires explanation. This discrepancy is greater 
than appears at first sight, for the "mean thermal unit" (over the range 100° to 0°) 
adopted by Bunsen is supposed to be greater than the "thermal unit at 15° ' 
adopted by Begnault during his researches into Latent Heat, and thus the divergence 
would be increased if both were expressed in terms of the same thermal unit. 

The doubt introduced by the above considerations is due to uncertainty regarding 
the comparative magnitude of the different thermal units and does not affect the 
value of Dieterici's experiments, although it renders his conclusions somewhat 
uncertain. 

There can be but little doubt that the mass of mercury expelled from a Bunsen 
calorimeter by the subtraction of a definite thermal unit is a quantity that can be, and 
doubtless will be, determined with accuracy, and if any correction on the conclusions 
arrived at by Bunsen, Schuller and Wartha, and Velten is found to be necessary, 
it can be applied to the values of the latent heat of evaporation at 0° obtained by 
Dieterici. 

This case well illustrates a matter to which I have before endeavoured to call 
attention ,j viz., that a mistake in thermometry is a fatal error in experimental 
work. It is impossible to correct the conclusions arrived at by the investigator, 
however our knowledge of thermometry may increase, since we should require to have 
in our possession the actual thermometer used by the observer, together with a full 
knowledge of the circumstances under which it was observed. As before remarked, 
Dieterici's results were independent of thermometry, hence their peculiar value. 

Begnault's formula for the " total heat of steam " has been so generally accepted, 
and the experiments upon which he founded it are so justly considered as examples of 
that singular skill and ability for which all his work is distinguished, that it is with 
diffidence that I venture to offer criticisms on his methods or conclusions. I would 
repeat that Begnault himself evidently attached less importance to his determina- 

* The actual values obtained by these observers were as follows : — Bunsen, 15'41 ; Schuller and 
Wartha, 15-442; Velten, 15-47 mg. ' Wied. Ann.,' vol. 33, 1888, p. 439. 
t ' Wied. Ann.,' vol. 37, 1889, p. 499. 
% ' Science Progress,' April, 1894. 
MDCCCXCV. — A. 2 M 



266 MR. E. H. GRIFFITHS ON THE LATENT 

tions at low temperatures than to those above 65° C In Table IV. of his paper, 
" Sur les chaleurs latentes de la vapeur aqueuse a saturation sous diverses pressions," 
are given the results of all his experiments below 63°, and in his introductory remarks 
to this table (pp. 712-719) he clearly indicates his comparative want of confidence in 
the results.* 

A searching criticism of Regnault's work is given by Winkelmann in ' Wied. 
Ann.,' vol. 9, 1880, and had the limits of this communication permitted it, I should have 
liked to quote several pages of that paper, but I will content myself with giving a 
short summary of his arguments. 

I would first remark that Winkelmann's object was to explain the discrepancy 
between what he terms the " theoretical density " of water vapour, and that which 
results from " the mechanical theory of heat." He assumes the former as 0"6225 ; 
but does not give the data by which he obtains that number (I find that if we take 
the molecular weight of H 3 as 17 "98, and the density of H as "06924 (air = I), we 
arrive at the same value). He then (assuming that J == 424) calculates the density 
from the thermodynamic equation L = T/J (*■' — s) cW/dT, by substituting for L — 

(a) the values resulting from Regnault's formula for the " total heat," viz., 

606-5 + -305t, 

(b) the values of L given by the equation 

L= 589-5 -0-2972^ -0-0032147i- + 0-000008147i 3 . . . . (W), 

the last being a formula constructed by Winkelmann, but based on Regnault's 
experiments at high temperatures. 

Winkelmann contends that not only does the use of (W) bring the values 
obtained by the '"' mechanical theory " into greater harmony with the " theoretical 
value," but also that the formula (W) is in closer agreement with Regnault's 
experiments than is the formula given by Regnault himself. 

True, the values obtained by Winkelmann are always greater than 0'6225, but he 
contends that it is impossible to imagine the real density as less than the " theo- 
retical." although it is easy to see that it may be greater. 

* " J'ai cherehe a obfcenir la chaleur latente de la vapeur d'eau a saturation aux basses temperatures 
par une autre methode qui me permettra, j'espere, d'obtenir cette donnee avec beaucoup d'exactitude et 
contre laquelle on ne peut pas elever les objections que nous avons faites contre le premier procede. 
Mais cette methode, que j'ai decrite a la fin de mon Memoire sur l'hygrometrie (' Annales de Chimie et 
de Physique,' 3 e serie, tome 15, p. 227), exige la connaissance de plusieurs donnees sur lesquelles il reste 
encore beaucoup d'incertitude. On a besoin notamment de connaitre la capacite calorifique de l'air et la 
quantite de chaleur que l'air absorbe pendant sa dilatation. II m'a paru necessaire de determiner ces 
deux elements par de nouvelles experiences, et c'est seulement lorsque celles-ci seront terminees que je 
pourrai calculer les determinations de la chaleur latente de la vapeur d'eau," p. 722. 



HEAT OF EVAPORATION OF WATER. 267 

When I give the results of my experiments, I think that I shall be able to show 
that Winkelmann in his desire to lower the value of L at low temperatures has 
considerably overshot the mark, and that in deducing the values at, or near, 0° from 
experiments above 65° he has carried the method of extrapolation beyond clue 
bounds. At present, however, I will only consider his reasons, with which I agree in 
the main, for rejecting Regnault's determinations at lower temperatures. 

(1) There is no doubt that Regnault's formula does not give the mean result of 
his experiments at low temperatures. In all, he performed twenty-two experiments 
at temperatures below 65° (Table IV., 'Memoir, de l'Acad.,' xxi., 1847), and the 
mean value given by these twenty-two experiments differs from that given by his 
formula by. 1*8. 

(2) The experiments above referred to were performed in a different manner from 
those at the higher temperatures. The water to be evaporated was placed in a 
spiral within the calorimeter, and the pressure reduced until the water boiled, the 
vapour being condensed in a vessel surrounded by ice. Regnault deduced the 
temperature of the water when evaporating by observing the pressure of the vapour 
in the condenser — hence, as Regnault himself says, " It is probable that the elastic 
force observed on the barometric manometer is decidedly less than the mean pressure 
at which the vapour is distilled," and thus the evaporation is taking place under a 
greater pressure and at a higher temperature than that given by his Table IV. 

Again, the temperature of the saturated vapour is sensibly beneath the tempera- 
ture of the calorimeter, and so lowers the temperature of the calorimeter more than 
would be done by the evaporation alone. 

In the case of other liquids, Regnault made a correction for the heat abstracted 
by the vapour while passing out of the calorimeter, but he did not apply this correc- 
tion in the case of water. It is true that no special arrangements were made to 
warm the vapour to the calorimetric temperature (as was done by coils with the 
vapours of other liquids), but there can be no doubt that the vapour must have 
abstracted heat from the walls of the calorimeter. 

Let k be the specific heat of the vapour, t the temperature at which evaporation 
takes place, t and t x the initial and final temperatures of the calorimeter, then the 
heat per unit mass absorbed should be k { -| (t + t^) — t } ; at the same time this is 
not a correction that can be applied with certainty. 

(3) At these low temperatures a small difference in the pressure of the vapour 
corresponds to a considerable difference in temperature ; thus, if the temperature of 
the water is deduced from the pressure in the receiver, the error may be considerable.* 
The effect of all these errors would be to make the value of L given by Regnault's 
experiments too great. 

The above criticisms do not apply to the experiments at the higher temperatures. 

* For example, a difference of 04 millim. at 4° would correspond to a difference of 1 U C. 

2 M 2 



268 MR. E. H. GRIFFITHS ON THE LATENT 

I think the preceding summary fairly represents the remarks of Winkelmann on 
the determinations at low temperatures.* 

I will now add some remarks of my own. 

Regnault was compelled to limit the duration of these experiments as much as 
possible, otherwise his correction for the loss or gain by radiation, etc. (which was at 
best but a somewhat uncertain one) became large as compared with the other 
magnitudes to be measured. The average length of an experiment was about five 
minutes, though in one or two extreme cases it extended to 11 minutes; in this 
time he evaporated about 5 "3 grams of water, and thus he was compelled to reduce 
the pressure in the condenser very considerably below the pressure of saturated 
vapour at the temperature of the calorimeter. He was, therefore, unable to diminish 
the sources of error (subsequently dwelt upon by Winkelmann) in the manner he 
might have done had he not been thus limited in time. Regnault, referring to the 
difference between the pressure in the condenser and in the calorimeter, writes as 
follows : " La difference entre les deux tensions doit meme etre assez grande ; car 
pour que l'experience se fasse dans des conditions favorables d'exactitude ; il faut que 
la distillation soit assez rapide, arm que la correction e ne soit jamais qu'une fraction 
tres- petite de t — ^."t 

Again, another matter of importance is the thermometry. On p. 692 (ibid.) he 
says : " Les thermometres a mercure des calorimetres ont etes gradues avec le plus 
grand soin, un degre centigrade occupe sur la tige du thermometre 

du calori metre C 18°7620 ; par suite 1° vaut 0°-053283. 

C 18°-5800 ; „ 1° „ 0°-053821. 

II est facile d'apprecier avec certitude le dixieme des divisions, c'est-a-dire -^o de 
degre centigrade dans les lunettes horizontales avec lesquelles on observe les 
thermometres." 

The only other reference is on p. 707, where he remarks that he reduced the 
readings from the mercury to the air scale by means of the table given on p. 239 of 
his paper "De la mesure des Temperatures. "J I have searched the paper throughout 
for some indication as to the thermometers actually used, in the hope that I might 
be able to identify them with some one of those of whose comparison with the air 
thermometer he gave an account in another paper ; but the above are the only 
references to the thermometry that I have been able to find. Had a direct com- 
parison between these thermometers and the air thermometer been made, it is most 
probable that Regnault would have mentioned it ; we may, therefore, assume that, 

* Had not Regnault measured the temperature of the evaporating water by means of the vapour 
pressure in the condenser, the above objections would lose their force, 
t 'Memoir, de 1'Acad.,' vol. 21, 1847, p. 716. 
+ ' Memoir, de l'Institut,' vol. 21, p. 220 



HEAT OF EVAPORATION OF WATER. 269 

knowing the nature of the glass, he simply reduced them to the air scale by the table 
above referred to. 

Throughout the low temperature determinations the temperature of the calorimeter 
fell during an experiment through about 5°'6 (in the greatest case 5°76l), and thus 
an. error of o, 01 in his thermometry would cause a difference of more than 1 in 600 
in the results. At higher temperatures, however, the average rise in the temperature 
of the calorimeter exceeded 12° and thus the effect of any such thermometric error 
would be considerably reduced. 

Again, the observations of the change in temperature of the calorimeter at low 
temperatures w r ere always taken on a falling thermometer. I have in a previous 
paper (J., p. 442) expressed my disbelief in the value of any observations of mercury 
thermometers when their temperature is falling. I am not alone in this opinion,* 
and it has been confirmed by subsequent experience. I am sure that inaccuracies of 
a much larger order than O- 01 would have presented themselves from this cause 
alone, and the great divergences observable amongst Regnault's individual experi- 
ments at low temperatures is I have no doubt partly attributable to this cause.t In 
all his experiments at higher temperatures, however, his thermometers were rising 
and the discrepancies between individual observations were much less marked. 

It will be noticed that the various sources of error which have been enumerated 
either disappear or are much diminished at the higher temperatures. 

Again, the ever-recurring difficulty with regard to the specific heat of water 
presents itself. The correction is not so simple as has been assumed by those who 
have merely applied Regnault's own formula for the specific heat of water to the 
expression for the total heat of steam, for the correction would have to be applied 
during the reduction of each separate experiment, as the quantity of heat absorbed 
by the calorimeter and contents when warming or cooling through a degree of 
temperature would vary according to the mean temperature of the range and the 
resulting correction would, I believe, be greater than is usually supposed. 

There appears to be but little doubt that Regnault's expression for the changes 
in the specific heat of water is inaccurate. As far as I know, Rowland (1877). 
Bartoli and Stracciati (1889), and myself (1892) are the only observers who have 
seriously attacked this difficulty since the time of Regnault, and all agree in one 
conclusion, viz., that the specific heat of water diminishes as the temperature rises to 
20°, and the methods of experiment employed by these observers were so entirely 
different that their agreement in this matter carries great weight. We cannot, 
therefore, accept without question Regnault's conclusions as to the changes at 
higher temperatures. The magnitude of the correction involved may be illustrated, 
as pointed out by Dieterici himself, by the following example. If we assume 

* Schuster and Gannon, Communication to the Royal Society, Nov. 22, 1894. 

t The comparatively slow rate of stirring would also tend to make the temperature measurements 
uncertain. 



270 ME. E. H. GRIFFITHS ON THE LATENT 

Rowland's value for the specific heat of water at 15° C, the difference between the 
thermal unit at 15° C. and "the mean thermal unit" over the range 100° to C , 
amounts (if we accept Dietekici's interpretation of Regnault's values) to nearly 
1-| per cent.,"" and would reduce the value of L at 0°, as given by Regnault's formula 
(viz., 606-5), beloiv the value found by Dieteeici (598'8).t 

The tacit assumption amongst physicists that the discrepancies arising from doubts 
as to the value of the thermal unit are so trivial that they may be disregarded is, as 
shown by the above example, much to be regretted, and the many efforts to deduce 
specific volumes, etc., from the equation J = L/T (s' — s) clpJdT, shows how frequently 
this difficulty is ignored. It is strange that, although so much attention has been 
devoted, during recent years, to the exact determination of various physical units, so 
little has been done with regard to this extremely important fundamental constant. 

The experimental difficulties are not so great as to prevent all progress, and 
I venture to appeal to the Royal Society to consider this matter ; indeed, I would 
go so far as to express my personal belief that the method of measuring small 
differences of temperature indicated in a paper read before the Physical Society 
last October removes many of the difficulties which have hitherto barred the way. 

It is, I think, evident that we are not justified in concluding that our knowledge 
of the value of the latent heat of evaporation of water at low temperatures is sufficient. 
It has been already shown that the effect of most of the causes of error above 
enumerated diminishes at higher temperatures ; and a study of Regnault's Tables I. 
to III. will confirm the conclusion that we may regard the results at those tempera- 
tures as of greater accuracy. Even at higher temperatures, however, the difficulties 
with regard to the measurement of differences of temperature and of the capacity for 
heat of water present themselves. 

I can find no record of experiments by any observer at temperatures between 16° 
and 65° C. 

The above considerations are, I think, sufficient to indicate the necessity of a 
re-determination of the latent heat of evaporation of water, at all events at low 
temperatures. 

Section III. — Description of the Method. 

I was anxious, if possible, to devise a method of such a nature that my results would 
not be appreciably affected by 

(1) errors in thermometry, 

(2) changes in the specific heat of water, 

(3) the capacity for heat of the calorimeter, 

(4) loss or gain of heat by radiation, &c, 

* At the end of this paper I give figures which lead to the conclusion that the difference between the 
" mean thermal unit " and the " thermal unit at 15° " is less than is usually assumed, 
t Dieteeici, ' Wied. Ann.,' vol. 37, 1889, p. 506. 



HEAT OF EVAPORATION OF WATER. 271 

and if these points are borne in mind they may serve to explain some of the con- 
trivances which might otherwise appear uncalled for. 

If the vessel in which the evaporation is taking 1 place is kept at a constant tem- 
pei-ature, we are independent of the capacity for heat of it and its contents ; we also 
dispense with the measurements of changes of temperature. Thus, if matters be so 
arranged that the loss and gain of heat throughout an experiment are balanced, many 
fruitful causes of error are avoided. Of course, the actual temperature of the calori- 
meter during evaporation must be determined, but a small error here is of little con- 
sequence. The change in the value of L (when L is the latent heat of evaporation of 
water) is small as compared with the changes in 9. In fact, an accuracy of an order 
of yjj of a degree would be sufficient when determining the actual elevation. 

The heat was supplied to the calorimeter by means of a wire whose ends were kept 
at a constant potential difference. The thermal balance could be maintained in one 
of two ways, 

(1) If the heat supply was too great, the electric current could be temporarily 

stopped : or, the rate of evaporation of the water increased. (The latter was 
the method that I generally adopted.) 

(2) If the cooling was too rapid, the only mode of maintaining the balance was (in 

the apparatus about to be described) to reduce the rate of evaporation. 

The water to be evaporated was placed in a small silver flask, connected with which 
was a spiral coil of silver tubing 18 feet in length. Both flask and spiral were within 
the calorimeter, and the water-vapour, after passing through the spiral, emerged from 
the apparatus at the temperature of the calorimeter. Surrounding the flask, and 
between it and the spiral, a coil of platinum silver wire was arranged, and flask, 
spiral and coil were entirely immersed, in aniline during my preliminary experiments, 
subsequently in a certain oil of which an account will be given later. 

The calorimeter (which was filled to the roof with the aniline or oil, and the equality 
of temperature maintained by rapid stirring) was suspended by glass tubes within a 
steel chamber, whose walls were maintained at a constant temperature. So long, 
therefore, as the calorimeter and the surrounding walls were at equal temperatures, 
there was no loss or gain by radiation, &c. If during an experiment the temperature 
of the surrounding walls changed, the method of experiment involved a corresponding 
change in the temperature of the calorimeter, and, thei-efore, some loss or gain of heat 
would be experienced. The apparatus was so designed that any such change in 
temperature was extremely small (in no case amounting to toTT°)> 7 e ^> m order to 
estimate the loss or gain, it was necessary to know approximately the capacity for 
heat of the calorimeter and contents. 

Small differences between the temperature of the calorimeter and the surrounding 
walls would, during an experiment, be of no consequence, provided that the oscillations 
were of such a nature that the mean temperature of the calorimeter was that of the 



272 MR. E. H. GRIFFITHS ON THE LATENT 

surrounding space, and I think I shall be able to show that this condition was 
fulfilled. 

In addition to the heat supplied by the electric current there is also a supply due 
to the work done by the stirrer. It was in the estimation of this " stirring supply " 
that I found my greatest difficulties, and I regard that portion of my determinations 
with the least confidence. Fortunately the heat thus generated was only about j^„ 
of the heat supplied by the current, and thus any small error in that portion of the 
work becomes of little account. 

Of the accuracy with which the electrical supply could be measured, there is no 
question, and I have but one remark to make on this portion of the subject, viz., that 
even if the values of the E.M.F. of my Clark cells, or the absolute resistance of the 
box-coils given by the standardisations performed during my determinations of J, are 
in any way inaccurate, such errors would eliminate, since the value of J was 
determined by means of the same standards as those by which the quantity of heat 
developed in these experiments was determined. Hence, by assuming my former 
value of J, I get the comparison in terms of a thermal unit at 15° C, independently 
of the numerical value of J assumed in the reductions. 

One further correction remains to be noticed. I have spoken of the temperature 
of the calorimeter as oscillating about the exterior temperature, and it might happen 
that at the close of an experiment this difference was not the same as that at the 
commencement — if any such difference existed. The magnitude of this correction 
depended, of course, on the ability of the observer to maintain the thermal balance. 
In these experiments the correction was extremely small, and in any case could 
be determined with great accuracy. 

Having indicated the nature of the observations I will proceed to state the relation 
between the various sources of loss, or gain of heat. 

Let Q,; be the thermal units per second due to the electrical supply. 
„ Q s „ „ ,, ,, „ mechanical supply. 

,. %q be the total heat supply during an experiment from any other causes. 

Then, if M be the mass of water evaporated, L the latent heat of evaporation 
a.t temperature 6, and if the electrical supply is maintained for a time t e , and the 
mechanical for a time t s , 

ML = Q e t e + QA + %q . . . (1). 

Now the D.P. at the ends of the coil was always some integral multiple of the D.P. 
of a Clark cell. 

Let e be the D.P. of a Clark cell, n the number of cells, and R x the resistance of 
the coil at the temperature 6 V then 

Q-=v • • • ( 2 )- 



HEAT OF EVAPORATION OF WATER. 



273 



If the calorimeter at the commencement and end of an experiment was at exactly 
the same temperature as the surrounding walls, then if their temperature was 
unchanged, the term 2$ would vanish ; but although this term throughout these 
experiments was of small dimensions, it could not be entirely ignored. 

Let 8' and 6" be the temperature of the surrounding walls at the beginning 
and end of an experiment ; suppose the calorimeter temperature (0^ to exceed the 
surrounding temperature by cl' at the commencement and d" at the end of an 
experiment. Then fall in temperature of calorimeter 

= (0' o + d')-(d" o + d"). 

Hence the heat given out by the calorimeter in conseqtience of this fall in tempera- 
ture is 

G* Wo + d') - (0" o + d")}, 

where C fli is the capacity for heat of calorimeter and contents at the temperature 6 V 

If we neglect any small loss by radiation, &c., due to the differences d' and d" 
between the temperature of the calorimeter and the surrounding walls, we may 
conclude that the whole of the heat thus evolved by the calorimeter was expended in 
the evaporation of water, hence 



Hence 



tq = c ei {(0'o-e" o ) + (d'-d")y* (3.) 



ML = 



e V x U 
P n J 



+ Q, x u + c S] {(d' - e\) + (d' - d")} . 



(4.) 



In order to convey an idea of the relative importance of the terms in equation (4) 
I will here give the approximate mean value of each term resulting from the experi- 
ments described in succeeding pages. 

Table II. 





QA. 


V^tf X ts* 


2?. 


When 

1 — 30 and n - 4 


2150 

2305 
1752 


19-2 

32-9 
32-9 


±1-6 

±1-2 
±1-2 



' This apparently clumsy method of representing the quantity of heat evolved or taken up by the 
calorimeter was adopted because, as the method of experiment involved separate determinations of 
0'o' 0"o> & an< l ^ "> the actual temperature of the calorimeter at. any time could only be obtained in this 
manner. 

MDCCCXCV. — A. 2 N 



274 MR. E. H. GRIFFITHS ON THE LATENT . 

Although, of course, I had, when commencing these experiments, no exact know- 
ledge as to the comparative values of the terms, some preliminary observations 
enabled me to form a rough estimation of their magnitudes and consequently of the 
degree of attention which should be devoted to their accurate measurement. 

Section IV. — The Method of Maintaining the Space surrounding the 
Calorimeter at a Constant Temperature. 

1 have, in Paper J., given an account of the apparatus employed for this purpose, 
and full details and plates will be found on pp. 374-378 (ibid.). 

In order, however, to give a general idea of the arrangements, and to save the 
reader the trouble of reference, I will here quote the brief description given in the 
abstract of that paper : — " The calorimeter was suspended within an air-tight steel 
chamber. The walls and floor of this chamber were double, and the space between 
them filled with mercury. The whole structure was placed in a tank containing about 
20 gallons of water, and was supported in such a manner that there were about 
three inches of water both above and beneath it. The mercury was connected by a 
tube with a gas regulator of a novel form, which controlled the supply of gas to a large 
number of jets. Above these jets was placed a flat silver tube, through which tap- 
water was continually flowing into the tank, all parts of which were maintained at an 
equal temperature by the rapid rotation of a large screw. Thus, the calorimeter may 
be regarded as suspended within a chamber placed in the bulb of a large thermometer 
— the mercurv in that bulb weighing 70 lbs. A change of 1° C. in the temperature 
of the tank- water caused the mercury in the tubes of the regulating apparatus to rise 
about 300 millims. Special arrangements were made by which it was possible to set 
the apparatus so that the walla surrounding the calorimeter could be maintained for 
any length of time at any required temperature, from that of the tap-water (in summer 
about 13 c C, in winter 3° C.) up to 40° C. or 50° C." 

I think the above summary, together with the section on Plate 4, will convey a 
sufficient idea of the apparatus. 

Since 1892, I have made certain improvements, which I will briefly describe. 

During my J. experiments the range of tempei'ature was from about 14° C. to 26° C. 
In subsequent experiments when I have required to use the apparatus at higher 
temperatures, it was found that the oscillations in temperature became seiious, in some 
cases amounting to -Jg° C. This was due to the temperature lag of the large mass of 
mercury, so that when the gas was lowered by the action of the regulator the resulting 
in-flow of cold water lowered the tank temperature before the mercury had contracted 
sufficiently to again, heat the in-flow. In Paper A. I have described as follows the 
arrangements made to meet this difficulty : — -"As now arranged, when working above 
temperatures about 20° C, a small motor acts as a heart, and, the tap-water being 
shut off, pumps the tank-water itself round through the silver tube placed above the 



HEAT OP EVAPORATION OF WATER. 275 

gas-jets. The water, by passing through the pump, &e., is slightly cooled; thus, the 
work of the regulator is confined to simply supplying the heat lost by convection, 
radiation, &c, and it performs this task admirably. As an illustration, I may mention 
that, in the series of over 50 experiments treated of in this communication, on only one 
occasion did the temperature of the steel chamber change by as much as too° C. 
throughout the duration of an experiment. On the solitary occasion that a change 
amounting to nearly -^q° C. was observed, the cause was found in the caking of the 
lime through which the gas was passed on its way to the regulator, and, in 
consequence, the experiment was discarded before working out its results." 

On account of the use of the differential thermometers (see Section V.) employed 
in the present investigation, it was essential that any changes in the temperature of 
the steel chamber should be measured with greater accuracy than was necessary in 
my previous tvork, for now such changes influenced the temperature measurements, 
whereas on former occasions they only affected the loss by radiation, etc. An open 
range mercury thermometer placed in mercury in the hole E (Plate 4) gave the 
temperature of the walls surrounding the calorimeter and changes in the mean stem 
temperature had to be guarded against for the reason above given. The small motor 
already referred to now served another purpose. A portion of the water raised by 
the pump, instead of returning to the tank through the silver tube passed into a coil 
of about 20 feet of " compo. " tubing inserted in the tank, was then forced up a glass 
tube surrounding the stem of the thermometer, and passing out at the top, returned 
to the tank. Thus the stem- temperature was kept constant throughout an experi- 
ment, the regularity of the flow being secured by an overflow system. True, the 
water near the top of the glass tube would be slightly cooler than the tank water 
when working at high temperatures, but this was of no consequence, as the chief 
use of the thermometer was to detect differences during an experiment. Two 
thermometers labelled A and II. were used. Although an accuracy of an order of 
Yq° C. would have been sufficient in actual elevation, I compared these thermometers 
every o- 5 G of their ranges with two different Tonnelot thermometers, standardised 
by the Bureau International des Poids et Mesures, and also with my own platinum 
standard. The results of the separate comparisons (expressed on the nitrogen scale) 
agreed within "005° O 

The stems of both thermometers were graduated in millimeti'es. A (range 16° to 
26° C.) having about 27 millims. per 1° C. and II. (range 28° to 53° C.) about 20 
millirns. per 1° C. A table was constructed for the whole range of temperature, 
giving the value in degrees C. of (a) each millimetre of these thermometers in terms 
of the air thermometer, and (b) in terms of the millimetres of the " mean bridge wire 
scale" used by me for the determination of differences of temperature. 

These thermometers were observed through a microscope fitted with a micrometer 
scale so divided that it gave 10 divisions to the millimetre. There was no difficulty 

2n 2 



276 MR. E. H. GRIFFITHS ON THE LATENT 

in estimating yg of the micrometer divisions, and thus readings could be taken to 
•01 millim., that is to about "0004° C. on A and to about '0005° C. on No. II. 

I do not, of course, claim that I could determine actual temperatures to this 
closeness, by these or any other mercury thermometers, but, owing to the precautions 
above described, I have no doubt but that changes in temperature of the order of 
o, 001 C. {i.e., about "025 millim.) could be detected, especially as any movement was 
extremely slow — in no case as much as o, 01 0. per hour. A constant vibration, 
due to the pumping of the water up the surrounding tube, tended to prevent 
" sticking." 

A further improvement has been the addition of a gas pressure regulator. This 
apparatus was designed for me by Mr. Horace Darwin, and is the only satisfactory 
instrument of the kind I have seen. It is most perfect in its action, and I am now 
absolutely indifferent to changes of pressure in the mains. 

With these additions, I think that the whole of this constant temperature portion 
of the apparatus may be considered as nearly perfect. Only those who have watched 
it actually at work can appreciate the certainty of its action ; it can be set with 
precision to any temperature between that of the tap-water and 64° (the highest 
temperature at which I have actually tested it), and my only regret is that cir- 
cumstances compel me to leave unused, for the greater portion of each year, 
apparatus by means of which so many difficulties could be overcome. 

Section V. — Description of the Calorimeter and its Connections. 

The calorimeter was made of brass and was of cylindrical form, 10 centims. in 
diameter and 10 centims. in height. 

It contained a silver flask, F (see Plate 5, fig. 1), in which the evaporation took 
place ; a stirrer, of which the lower end only is shown at S ; a rack (shown in the 
horizontal section, Plate 5, fig. 2) which carried a coil of platinum-silver wire, and 
about 18 feet of silver tubing wound in a spiral — shown in section at p.j) '. A 
platinum thermometer also passed from the top to the bottom. With so many 
objects crowded into so small a space, it is difficult to convey any clear idea of the 
internal arrangements, therefore I will only attempt a brief description, and shall 
rely chiefly on the sections given in Plate 5 to convey the necessary information. 
The capacity of the flask, F, up to the side opening at d, was about 68 cub. centims. 
Any vapour or gas passing from the flask into the spiral at d, after descending to the 
bottom of the calorimeter, ascended throughout the whole length of the coil, and 
thence up the tube e. This arrangement was adopted to diminish any chance of the 
carrying of the liquid, or " priming," by the flow of vapour or gas, as it appeared 
improbable that particles of liquid would be carried up a gentle slope of 18 feet in 
length. 



HEAT OF EVAPORATION OF WATER. 277 

Any inflow of gas came down the tube f, and passed directly into the bottom of 
the flask at g. 

The stirrer S had two paddles, reaching from top to bottom of the flask ; the 
blades and the central tube were of thin copper. Down this tube passed a steel 
shaft, which hung at the lower extremity within a hole in a sheet of brass projecting 
from the side of the calorimeter. The bearings of the stirrer were entirely outside 
the calorimeter, and the lower end did not touch the base, or bear on the surrounding 
plate, whose only purpose was to check vibration. The paddles had a slight "pitch," 
so as to throw the liquid upwards, as well as cause it to rotate. The exterior 
bearings at the top of the glass tube S (fig. 3) were of the kind figured in Plate 2, 
Paper J., and were certainly sufficiently air-tight to prevent any diffusion, even when 
the stirrer was rotating rapidly, but, as the calorimeter was filled with a non-volatile 
liquid, the air-tightness of this joint was of little consequence, especially as the tem- 
perature of the calorimeter remained constant during the experiments and the air- 
space above the liquid was small. The rubbing surfaces were very true and always 
immersed in oil, thus the heat generated must in any case have been unimportant. 
The greater portion of any heat developed in the external bearings would pass to the 
brass tube, of which they formed a part, and, as the lower portion of this tube was 
washed by the tank water, its temperature would in any case rise but little. Any 
heat passing down the steel shaft (length 28 centims., diameter 0*35 centim.) would, 
of course, be included in the "stirring correction," but I should imagine that it was 
in reality negligible, for about 4 inches of the glass tube down which it passed were 
also washed by the tank water. 

Further, slightly above the top of the calorimeter a section of ivory was inserted in 
the stirring shaft, in order to diminish conduction as much as possible. 

The platinum-silver coil was wound on small ebonite tubes surrounding the narrow 
brass pillars of the rack, whose section is shown at R (fig. 2). The method by which 
the insulation of the rack was maintained, where the two brass pillars R 3 R 2 passed 
through the top of the calorimeter, is shown by the section (Plate 5, fig. 4). It must 
be remembered that these junctions had not only to be perfectly insulated, but that 
they had also to be absolutely air-tight, over a considerable range of temperature (l 0° to 
60° C.), # even to pressures of 1 atmosphere. 

The platinum-silver coil was about 100 centims. in length, and so wound that it 
was completely immersed when the depth of the liquid was 4 centims. Two copper 
wires (B.W.G., 21) were soldered to each of the pillars E, l and B 2 where they projected 
above the roof of the calorimeter at / and V (fig. 3), thus, in the steel lid, there were 
four junctions similar to those above described (see Plate 6, fig. 3). The blocks of 
ebonite forming the top slab of the junctions were, however, in this case, made 
nearly five inches in length ; they projected as far as the lid of the tank, and 

* The insulation of the whole circuit after all the apparatus was placed in position, was better than 1 
could measure, i.e., 10 7 ohms. 



278 MR. E. H. GRIFFITHS ON THE LATENT 

thus all contact between the leads and tank-water was prevented. The calori- 
meter was hung below the steel lid by five glass tubes, thus ten air-tight junctions 
of glass to metal were required, in fact, four of these junctions were, in reality, 
double ones, for the lower extremities of the narrow tubes e and f (Plate 5, fig. 1) 
had not only to be fixed into the lid of the calorimeter, but also joined on to the 
ends of the silver tubing. In like manner, where they passed through the steel 
lid, they had to join also on to glass tubes leading to two glass taps immersed in 
the outer tank. There were, therefore, practically fourteen such joints. I have 
previously described an alloy by which I was enabled to make these joints absolutely 
air-tight.""" In order to show how carefully all these joints were tested, as well as 
several others in the external connections by which communication with the mercury 
pumps was established, I extract the following from Paper A. : — "In the spring of 
this year the intra-mural space was exhausted until the reading of the McLeod gauge 
connected therewith was reduced to 11, indicating a pressure of about 0*12 millim. 
The apparatus was then left untouched for a month, except that the temperature was 
occasionally raised or lowered, and at the end of that time the reading of the gauge 
was still less than 12. Dry air was then re-admitted to this space, and the silver 
flask, with its connecting tubes (embracing about 50 feet of tubing with several joins), 
tested in a similar manner. Those who have had to deal with low pressures will 
understand that, when all was found satisfactory, a great difficulty had been sur- 
mounted. I did not retain this vacuum during the experiments, as I felt that it 
would subject the glass tubes, &c, to a continuous strain which the conditions of the 
experiments rendered unnecessary. The labour had not been lost, however, for I was 
able to count with confidence on the gas-tightness of the whole apparatus." 

Where the supporting glass tubes entered the calorimeter lid (as shown by the 
plan, Plate 5, fig. 3), they were surrounded by metal tubes (shown by the outer ring 
in each case) nearly 1 centim. in length which had their lower extremities soldered to 
the lid. The annular space between these and the glass tubes was filled with the 
alloy and the joints on the top of the steel lid, from which the apparatus hung, were 
of the same kind but slightly deeper. The tube S suiTounded the stirrer shaft. The 
platinum thermometer AB passed down T, and this tube was also used for inserting 
or withdrawing the calorimeter liquid. The thermometer was wrapped with india- 
rubber tape so that the annular space between it and the glass tube T was made 
air-tight throughout the upper 4 inches. 

Through h' h communication was established between the exterior and the 
silver flask. During my earlier experiments a thermometer stood in this tube 
with its bulb nearly at the bottom of the flask. It was of course possible to 
render air-tight the connection between the thermometer stem and the top of 
the tube h', where the latter projected above the tank. This would not, however, 
have been sufficient, for the flask contained a volatile liquid, and distillation would 

* ' Cambridge Phil. Soc. Proc.,' 1893. 



HEAT OF EVAPORATION OF WATER. 279 

have taken place into and out of the annular space between the tube and 
thermometer stem, according- as the calorimeter was warmer or cooler than the 
tank water. This thermometer had also to be frequently removed in order to 
insert liquids into the flask, and therefore any junction at the bottom could not 
be made a permanent one. The difficulty was surmounted as follows : — The 
silver tube h (Plate 5, fig. 1), which passed up from the lid of the silver flask 
was soldered to the calorimeter lid, above which it projected. A hollow brass rod 
just fitting the glass tube, but with its lower end tapered, was, before fixing the glass 
in place, held vertically with the tapering end filling the open end of the silver tube. 
The annular space between the silver and surrounding brass tube was then filled 
with the melted alloy, to above the top of the silver, and the glass tube lowered into 
its final position. When the alloy hardened, the brass rod was loosened by lowering 
into it a red-hot wire. The lower inch or so of the brass rod having been cut off was 
then placed co-axially round the thermometer stem and made one with it by filling 
the annular space between it and the stem with the same invaluable alloy. Thus, on 
lowering the thermometer into its place, the brass tube almost exactly fitted into the 
ring of alloy at the bottom of the glass tube. The fit was made good by prolonged 
grinding with rotten stone — -using the thermometer stem as a rotating shaft. The 
result was a practically air-tight join at the calorimeter lid. It must be remembered 
that as the air-tightness was secured by the cork at the upper end, this joint had not 
to stand any pressure, but was only required to prevent diffusion. 

I have, for two reasons, fully described this method of fixing the tube. (1) I 
thereby overcame a difficulty which had perplexed me for a long time ; (2) it was 
necessary to explain the constriction at the lower end of the tube h, which in its turn 
became a source of difficulty when I altered my method of experiment. 

Z and l x (fig. 3) are the insulating junctions for the rack on which the coil 
was wound. 

The base of the calorimeter, which was not fixed until everything else was in 
place, was heated until solder contained in the circular trough, of which a section is 
ghown at M (fig. l), became fluid; the calorimeter was then pressed down upon it, 
and, as soon as the solder commenced to harden, the cakmmeter was set in cold 
water. The base was thus soldered on without melting the alloy in the lid or 
injuring the internal fittings. 

The whole apparatus was a difficult and complicated one to construct, and I owe 
my sincere thanks to Mr. Thomas for the ingenuity and patience he devoted to the 
task. My brief description can convey but little idea of the many difficulties that 
had to be surmounted between the conception and completion of this apparatus, and 
I may mention that although commenced in February, 1893, it was not until the 
spring of this year (1894) that the calorimeter could be regarded as completed. 



280 MR. E. H. GRIFFITHS ON THE LATENT 

Exterior Connections. 

The upper end of the narrow glass entrance tube f (Plate 5, fig. 1) was, as before 
stated, connected with a glass single-way tap, T 3 (Plate 6, fig. 1), which, on the 
further side was connected with about 30 feet of thin-walled copper tubing immersed 
in the tank water. Thus, all gas entering the silver flask through T 3 would be 
at the temperature of the tank water, and (the calorimeter temperature being 
identical with that of the tank) no heat would be added or subtracted when gas was 
passed through the flask and spiral. T 4 was a four-way tap on the exit side, the 
arms of the one passage through its core being at right angles to each other. The 
tap is shown in fig. 1 {infra). A is the tube leading from the flask and connected with e 
(Plate 5, fig. 1). By rotating the core, A could be connected with B or D, or C 
could be connected with B or D. The glass tubes forming the outer case of both 
taps T 3 and T 4 were sealed at the lower extremity, and after a portion of the tube 
above the core had been filled with mercury, these taps were perfectly air-tight. 
The outer glass tube of each was about 6 inches long, thus the lower 4 inches were 
below the surface of the tank water, and the upper parts of the tubes were packed 
with cotton wool. The cores narrowed to a glass rod, which, passing through the 
wool, projected above the tank lid, where a handle was attached ; thus the taps 
could be opened or shut from the exterior of the whole apparatus. The position of 
the taps is indicated in Plate 6, fig. 1. 

Tube B (fig. infra) which communicated with the apparatus into which, during 
my earlier experiments, the vapour was passed, extended under the surface of the 
water to the walls of the tank, it then passed above a row of small gas jets, and thus 
no condensation took place until the vapour arrived at the drying bulbs. At the close 
of an experiment a movement of the tap connected C and B, and as C was connected 
by a three-way tap (T 2 , Plate 6, fig. 1) with the dry air supply, any moist air 
remaining in B or its continuation was swept into the receiving apparatus. On the 
other hand, by connecting A and D before the commencement of an experiment the 
vapour brought by the gas which had passed through the calorimeter was disposed of 
without affecting the weight of the receiving apparatus attached to B. Thus an 
experiment could be started at any moment by changing the connection at tap T 4 
from AD to AB, and that without altering in any way the conditions as to flow 
of gas, rate of evaporation, &c. 

Finally, I would remark that throughout the gas circuit, the gas only came into 
contact with the following materials — glass, silver (only hard solder was used for all 
the flask and tube connections), the glass-metal -joining alloy at the junctions, and the 
drying agents. True, in my " exhaust " experiments with water the vapour had to 
pass through about half-an-inch of thick rubber on the exit side, where connection was 
made with the condenser, but when using other liquids, this joint can easily be 
replaced by a glass one. "When evaporating ether (with which I have made some 



HEAT OF EVAPORATION OF WATER. 



281 



preliminary experiments), the grease on the cores of the glass taps was replaced by a 
trace of phosphoric acid, which appeared to answer admirably. Thus, the apparatus 
can be used without alteration for all volatile liquids which do not act on the metals, 
a possibility I kept steadily in view when designing it. 

Fig. I. 
Four way tap T 4 




[May 4, 1895. — At the meeting of the Physical Society on January 11, 1895, 
Professor R,amsay exhibited an apparatus by means of which the comparative latent 
heats of evaporation of different liquids could be determined. I had the pleasure of 
seeing the apparatus at work, and from that time I abandoned all idea of extending 
my own investigation to other liquids than water. The method adopted by Professor 
Ramsay is so perfect, and at the same time so simple, that I feel that it would be 
waste of time and energy to pursue my absolute determinations. I mention this 
because many of the precautions described in the preceding sections were adopted 
with the view of conducting experiments with various liquids, and (as I now discover) 
might have been dispensed with. 

Professor Ramsay now informs me that, although certain practical difficulties in 
the working of his apparatus have not as yet been entirely overcome, he has already 
determined (approximately) the comparative latent heats of evaporation of a con- 
siderable number of volatile compounds, and that the results will shortly be 
published. 

I venture, however, to call attention to the fact that the very perfection of 
Professor Ramsay's method increases the importance of an accurate knowledge of the 
absolute latent heat of evaporation of water.] 



mdcccxcv. — A. 



2 o 



282 MR. E. H. GRIFFITHS ON" THE LATENT 

Section VI. — The Determination op $q. 

I will now describe the method of obtaining the value of the various terms in 
Equation I. (p. 272) by which the quantity of heat supplied during an experiment is 
ascertained. 

~£q is the quantity whose accurate determination presented the greatest difficulty, 
therefore the apparatus was so designed as to reduce this term to as small dimensions 
as possible, and since many of the contrivances adapted to this end may, unless their 
purpose is explained, appear unnecessary and cumbersome, I commence with this term 
in order to avoid repetitions. 

Had it been possible to so arrange matters that the temperature of the calorimeter 
at the beginning and end of an experiment should be absolutely unaltered, this term 
(tq) would have vanished, and in my earlier experiments, during which I endeavoured 
to determine the mass of water evaporated by passing the resulting vapour through 
drying bulbs, this condition was practically fulfilled, since it was always possible to 
stop an experiment at any time. I was compelled, for reasons which will be given 
later, to abandon this method of estimating M, and to adopt a method in which a 
given mass of water was to be evaporated. The observer had, therefore, no choice as 
to the time when the experiment should be completed, and as the thermal balance 
could not be absolutely maintained throughout an experiment, it was impossible to 
ensure the identity of the initial and final temperatures. 

It was advisable, if possible, to so arrange matters (I.) that a small alteration in the 
quantity of heat should produce a considerable change in temperature, so that small 
differences in the thermal equilibrium might render themselves evident; (II.) that the 
oscillation in temperature might be reduced to as small dimensions as possible ; (III.) 
that the difference, if any, between the initial and the final temperatures should be 
accurately measured. 

Although Nos. I. and II. appear contradictory, such is not the case, for the 
important matter was to ensure the equality of the thermal, as distinct from the 
temperature balance ; therefore, if small alterations in the former made themselves 
readily evident by changes in the latter, and if the latter changes were kept small, 
the desired end was attained. 

Within the calorimeter there were two agencies at work — the cooling- due to the 
evaporation (which for convenience I shall henceforth venture to speak of as a "supply 
of cold "), and a supply of heat due to the current ; therefore, unless some means were 
adopted of rapidly bringing the contents to a uniform temperature, the temperature 
gradient from the hotter to the colder portions would be considerable. It was thus 
necessary to completely fill the calorimeter with some liquid and to rapidly stir this 
liquid. 

Two objections to the use of water immediately presented themselves : (a) its great 
capacity for heat (which would have caused changes in the thermal balance to have 



HEAT OF EVAPORATION OF WATER. 283 

bat a small effect on the temperature); (b) its electric conductivity, which would have 
necessitated the covering of the platinum-silver coil with some insulator. 

I therefore gave my first attention to the selection of some more suitable liquid. 
The ideal one ought to have small " volume heat,"* and should be a perfect insulator, 
and therefore I at first selected aniline. I determined its specific heat over a range 
of from 15° to 52° C, and found that in some respects it suited my purposes admir- 
ably. A full description of this work will be found in paper A. 

Early in September I had, in consequence of an accident, to take the calorimeter to 
pieces and withdraw the aniline. I was then alarmed by tlie darkening in colour 
which it had undergone. In the discussion on the paper above referred to, Dr. 
Armstrong expressed his opinion that the change in constitution indicated by this 
change in colour was not of a nature to render it likely that it would produce any 
appreciable effect on the specific heat, as it was probably due to the formation of a 
body whose properties were similar to those of aniline. I may add that Professor 
Ramsay independently expressed an opinion to the same effect. My observations 
show that no alteration in the specific heat of aniline had been indicated by the 
change in colour referred to, and I am still of opinion that it may be regarded as a 
liquid admirably adapted for calorimetric purposes, as it is but rarely that it would 
be required for experiments extending over a period of months or years. 

If I am able to carry out my investigations into the latent heat of evaporation of 
water and other liquids according to the plan I have designed, it is probable that the 
enquiry will occupy my leisure time for some years, and as the exact determination of 
the capacity for heat of the calorimeter and contents throughout a large range of 
temperature is a most laborious one, I was anxious to employ some liquid about the 
constancy of whose composition I should have no anxiety. 

At this time, Mr. Thomas suggested to me that I should t r y a particular kind of 
petroleum oil supposed to consist of hydrocarbons only. This is a singularly limpid 
oil, without colour, smell, or taste. I tested its insulating powers very severely over 
a range of temperature 10° to 150° C, and although I placed two large electrodes 
within a quarter of an inch of each other, and used a potential difference of 10 volts, 
I could cause no permanent deflection in a high resistance galvanometer throughout 
this range of temperature. Its specific gravity at 15° is '865, and, as I shall show 
hereafter, its " volume heat " is smaller than that of aniline. t After several 
experiments of different kinds, I came to the conclusion that this oil was a most 
suitable liquid for my purpose.^ 

The replacement of aniline by oil necessitated a re-determination of the capacity 

* I propose to use the above term to denote the capacity for heat of any volume of a substance as 
compared with the capacity for heat of an equal volume of water. The phrase has already been used in 
a similar sense by Deeley, ' Chem. Soc. Journ.,' 1893, p. 854. 

f This oil appears to me to be well adapted to many physical purposes. 

\ See note at end of this Section. 

2 O 2 



284 



MR. E. H. GRIFFITHS ON THE LATENT 



for heat of the calorimeter and its contents throughout my range of temperature, and 
as far as regards the purposes of the present enquiry, a great portion of my work on 
aniline was rendered useless. The method employed during the aniline investigation 
necessitated a repetition of the experiments with different masses of aniline and with 
different electromotive forces. As, however, those experiments had given me a very 
exact determination of the capacity for heat of the calorimeter itself throughout the 
range of temperature 15° to 52° C, the whole of the labour had not to be gone 
through again, for (the " water equivalent " of the calorimeter being known) it was not 
necessary, when using oil, to repeat the experiments with different masses. 

In Appendix II., I give particulars of the method employed for determining the 
capacity for heat of the calorimeter and contents at different temperatures. 

The following table gives the results, and as the value of the specific heat of this 
oil at different temperatures may be of use to other experimenters, I have also given 
(in terms of a thermal unit at 15° C.) the capacity for heat (C 6i ) of calorimeter and 
contents at temperature 6 X (N scale), and the specific heat of the oil Sj. The mass of 
oil (corrected to vacuo) = 474"02 grams. 

Table III. 



e v 


C, 


Si- 


•4830 + (6 l - 20) x -00087. 


o 

20 
30 

40 
50 


307-50 
312-38 
31779 
32314 


•4830 
•4917 
•5006 
•5092 


•4830 
•4917 
•5004 
•5091 



The tables in Appendix II. show that the numbers in Column III. are direct 
experimental results, not " smoothed " in any way. 

It is noticeable that the value of S : is a linear function of 6 1 throughout the above 
range, although the curvature of the line giving the capacity for heat of the 
calorimeter is very marked. 

Probably these results are correct to better than 1 in 1000 (see Appendix II.), but, 
as an inspection of Table II. will show, an order of accuracy of 1 in 10 would have 
been sufficient. As, however, the accurate determination of (\ and Sj involved (by 
the method adopted) little more labour than an approximate determination, I thought 
it advisable to ascertain the specific heat of the oil with accuracy. 

Since $q = C, {(0' o - 6" a ) + (d' - d")} and (\ varied from 307 to 323, it is 
obvious that if %q was to be kept small, the changes in o and d must be very 
limited, and that such changes must be measured with extreme care. Having 
already described the manner in which the temperature of the surrounding walls was 
kept constant, and the way in which any small variations in 6 were ascertained, 
I now indicate the method of measuring the values of d' and d" {i.e., the initial and 



HEAT OF EVAPORATION" OF WATER. 285 

final differences between the temperature of the calorimeter, Q x , and that of the 
surrounding walls, # ). 

As differences of temperature had now to be dealt with, the use of differential 
thermometers naturally suggested itself. 

The following extract is taken from a full description of these thermometers given 
in my Paper A. (see also Plate 6, fig. 2) : — 

" Two platinum thermometers (labelled AB and CD) were constructed with great 
care ; four stout platinum leads passed down the stem of each, supported and 
insulated in the usual manner by small disks of mica, and the resistance of all these 
leads was made as equal as possible before attaching the coils. Great attention was 
given to this matter, and it is probable that the leads in no case differed amongst 
themselves by 1 in 10,000. The coils, consisting of a particularly pure sample 
of platinum wire, were then attached, and several days were devoted to securing 
their equality Their resistance in ice was about 18 ohms, thus x^q-q of their 
resistance could be directly determined on the box. The galvanometer swing was 
about 500 for a change of "01 in the box ; and such equality was secured that when 
both thermometers were placed in ice (the necessaiy precautions being taken with 
regard to exterior connections, &c.) no readable difference in the swing of the 
galvanometer could be observed ; thus they differed by a quantity certainly less than 
1 in 100,000. This equality, although not a necessity, was a great convenience. 

" Although cut from the same length of wire, and insulated in a precisely similar 
manner, the coils did not possess exactly the same coefficients. The resistances in 
steam and sulphur were repeatedly determined and checked by observations in the 
vapour of aniline. Both thermometers were on several occasions heated to a red 
heat, the hard glass tubes containing them becoming slightly bent in the process ; 
but, since this annealing, no further change has been observable in them. The method 
of completely standardising such instruments has been fully described by Professor 
Callendar and myself in 'Phil. Trans.,' 1891, A, and I need not, therefore, here 
dwell upon it. The values of 8 differed slightly, viz., 1 - 513 and 1*5 11 ; but such a 
difference, even if not allowed for, would, over the range 0° C. to 100° C, in no case 
cause an error exceeding about 2-^00° C. in elevation. These thermometers were so 
connected that the compensating leads of AB were placed in series with the coil of 
CD, and vice versd. Any heating of the stem of AB or CD, therefore, added an 
equal resistance to each arm of" the bridge '; and, as the leads were everywhere bound 
together, the indications were absolutely independent of all changes in temperature 
except those of the bulbs. 

" The two thermometers, with their leads connected as described, were placed at 
opposite ends of a bridge- wire of platinum-silver. During the spring of this 
year this wire was subjected to a most careful calibration by what was practically 
Carey Foster's method, and it proved to be more unequal than I had expected. It 
was therefore re-calibrated by a different method in which a resistance-box was used 



286 MR. E. H. GRIFFITHS ON THE LATENT 

as a shunt, and the agreement between the results was satisfactory. The whole wire 
was 80 centims. long and had a total resistance of about 0"4 ohm. For convenience, 
and to avoid thermal effects, a similar wire connected with the galvanometer was laid 
alongside it, and the sliding-piece was fitted with a screw so arranged that a small 
turn of the screw-head made contact with both wires. 

"The wire and contact maker were covered by a thick copper shield (the screw- 
head projecting through a narrow slot) passing from end to end of the bridge. Thus 
the temperature of the wire was kept uniform. By means of a vernier, the divisions 
on the scale could be read to yo nullum, which with this wire and thermometers AB 
and CD indicated at 50° C. a temperatui'e difference of '000915° C. The temperature 
coefficient of this wire was found to be "00029. The resistances of the different parts 
of the wire were, after correction for the errors of individual coils, &c, merely expressed 
in terms of the mean box ohm, the absolute value being of no consequence so long as 
the fixed points were determined in terms of the same standard. The remaining two 
arms of the bridge were constructed of german-silver. They were wound together, 
boiled in paraffin, placed in a bottle, and I expended much care in finally adjusting 
them until equal. Their resistance was about 5 ohms, and that of the galvanometer 
about 8 ohms, which, assuming the resistance of the thermometers as about 20 ohms 
each, would give nearly the maximum of sensitiveness. A single storage-cell was 
always used, and a resistance of 40 ohms was placed in the battery ch'cuit when the 
thermometers were in ice. A table was then calculated which gave the resistance 
necessary in the battery circuit when the thermometers were at any temperature in 
order that C 2 R (where B is the thermometer resistance) should be constant. Thus 
the rise in the temperature of the thermometer-coils due to current-heating was 
always the same, and consequent errors were eliminated, a point to which I attach 
considerable importance. 

" The value of B : — B in thermometer AB was G'88815 ; therefore a difference of 
1 ohm at 50° C. indicated a difference of 14 0, 51 77 C, and as 

dpt f „ 2t - 100] 

the degree value of any bridge-reading at other temperatures can be deduced. 

" There was no difficulty, in the arrangement above described, of reading with 
certainty a difference of I q ° C, and, as an illustration, I may mention the fact that 
if the thermometers were placed in separate hypsometers side by side on the bench 
and one of the hypsometers was then removed to the ground (about 3 feet below), 
the difference in the bridge-wire reading thus caused slightly exceeded - 4 millim." 

In the paper above referred to, further particulars are given regarding the 
standardisation of these thermometers. During the experiments there described 
they were used to determine the rate of rise in the temperature of the calorimeter, 
whereas, in the work I am now describing, they were used chiefly as detectors of any 



HEAT OF EVAPORATION OF WATER. 287 

difference of temperature between the calorimeter and the surrounding walls, and I 
therefore omit the details of the determination of their fixed points, &c, although I 
must add some other facts which are of importance for the present purpose. 

The bridge-wire scale was so fixed that the mark 60 centims.* fell exactly in the 
middle. Had the bridge-wire been uniform therefore, and had the coefficients of the 
two thermometers been always the same, then when both were at the same tempera- 
ture the bridge- wire reading would necessarily have been always 60 centims. I 
have stated that the thermometer resistances might be regarded as practically equal 
when both were in ice. The bridge-wire reading, however, was found to be 5 98 '35 
millims., when AB and CD were both in ice. At first sight this appeared to indicate 
a difference in the resistances of the two thermometers at 0°, but when the 
calibration of the bridge was concluded, it gave 598'4 millims. as the middle point of 
the bridge and thus afforded independent proof of the truth of the calibration and 
of the equality of the coils forming the other two arms of the bridge. Owing to the 
slight difference above referred to in the coefficients of the two thermometers the 
reading of the bridge null-point was found to be 601 - 4 millims. when both thermo- 
meters were at 100°. Now (as described in Paper A.) the fixed points of these 
thermometers in ice, steam, aniline, and sulphur-vapour, had been repeatedly 
determined with extreme care. I have, since the conclusion of these experiments 
(i.e., on November 4), again taken the values of R and B^ — ice and steam. They 
remain practically unchanged and are as follows : — 





AB. 


CD. 


R, . 


. . 24-58526 


24-58333t 


R . 


. . 17-69711 


17-69720 



R 1 -B = 6-88815 6-88613 

Thus the difference between AB and CD would, when in steam, exceed their 
difference in ice by '00198 ohm. Now the value of 1 millim. of the bridge-wire at 
reading 60 was l - 0020 times the mean bridge-wire millim., and the value of the 
mean bridge millim. was '00062875 box ohm. Thus 1 millim. of bridge-wire at 
60 = '0006300 box ohm. Hence the -movement of the two thermometers from 
ice to steam ought, according to the standardisation, to have caused a movement 
of - 6 -^ millims. = 3'1 millims. On placing both thermometers in steam a,t 100° the 
actual bridge-wire reading was found to have altered from 598'35 to 601*40, a 

* The scale was marked from 20 to 100 centims. 

+ Expressed after correction for individual coil errors, &c, in terms of my " mean-box " ohm 
(Paper J., p. 409). The absolute values being of no consequence, I have, in order to save arithmetic, 
expressed the resistances of all my platinum thermometers in " mean-box " ohms. 



288 MR. E. H. GRIFFITHS ON THE LATENT 

change of 3 "05 millims. ; thus, entirely independent methods agree in giving the 
following formula as a sufficiently close approximation for the bridge-wire null-point 
at any temperature 0, viz., 

N.P. = 598-35 + '03d. 

True, the coefficient of 6 should be slightly larger, but I did not profess to read the 
vernier to nearer than "05 millim. during the calibration of the wire, and therefore 
any closer approximation would be useless. 

As even a small difference between the average temperature of the calorimeter 
and the surrounding walls would have some effect in experiments lasting more than 
an hour, the agreement between the results obtained by the different methods above 
described was extremely satisfactory. In addition I carried out a series of observa- 
tions with both thermometers strapped together and immersed in the rapidly- 
stirred tank water, the temperature of which was gradually raised from 15° to 54°, 
and the position of the bridge-wire null-point was found throughout that range to 
be accurately given by the above formula. 

The galvanometer was observed by means of a microscope fitted with a micrometer 
eye-piece by Zeiss. The swing was very " dead beat " and very uniform for a 
given D.P. The ygth of a division could be estimated without difficulty by anyone 
accustomed to the instrument, and it was found more convenient to read and enter 
swings with y^th of a division as unity rather than to express the fractions as decimals. 
Thus a swing of 2"5 divisions was entered as 25. I mention this as otherwise 
the swings given in the tables might appear curiously large. Occasionally the 
swing due to a change of 1 millim. in the bridge-wire reading was observed, but as 
the E.M.F. used was constant, and the galvanometer control -magnet was not 
re-adjusted during these experiments, the swing for a given change was found 
to remain practically constant when the temperature of the thermometers was 
unchanged. As the resistance of two arms of the bridge altered when 6 altered, the 
swing vai'ied slightly when 6 changed, but the arrangement, above described, for 
keeping C 2 R constant, diminished the extent of this change. A swing of 90 corre- 
sponded to a change of 2 millims. in the bridge-wire reading when 6 = 40°, and the 
swing at 30° was about 94. 

The swing was of course obtained by reversing the battery connections and was 
thus independent of thermal effects, changes in the position of the galvanometer 
zero-point, &c. 

Now, as above stated, a change of 1 millim. of bridge-wire about the reading 
60 centims. indicated a difference of "0006300 box ohm. If therefore the bridge- 
wire reading was at the null-point a swing of 10 indicated a difference of f of 
•0006300 = "000140 ohm in the resistance of the two thermometers. 

The following Table (calculated from the constants of the thermometers by means 



HEAT OF EVAPORATION OF WATER. 



28'J 



of the formula on p. 286) gives the change in temperature (on the N scale) corre- 
sponding to a change of O'l box ohm in thermometer AB*. 

Table IV. 



Temp. 


AR (box ohms). 


Apt. 


A0. 


o 

20 


01 


O 

1-4518 


o 

1-4387 


30 


01 


1-4518 


1-4430 


40 


o-i 


1-4518 


1-4474 


50 


o-i 


1-4518 


1-4518 



Now the value of the mean millimetre of the bridge-wire (at temperature 15°) was 
"00062875 box ohm, hence the following Table which (col. 2) gives the difference in 
6 indicated by a difference of 1 mean bridge-wire millim. from the bridge- wire null- 
point at the given temperature, and (col. 3) the difference in temperature indicated 
by a swing of 10 when the contact-maker is on the null-point. 

Table V. 



Temp. 


A0 for difference of 1 mean 
millim. b.w. 


A0 for swing of 10. 


o 

20 
30 
40 
50 


o 

0-009046 
0-009073 
0-009101 
0-009128 


0-001865 
0-001930 
0-002022 
0-002074 



Before an experiment, the contact-maker was set, with the aid of a magnifying 
glass, to the exact null-point corresponding to the temperature at which the experi- 
ment was to be conducted, and it was left untouched throughout the experiment. t 

The initial and the final swing rarely exceeded 30 or 40, and could certainly be read 
with a limit of error of 2, when only one observation was taken, and as, at these 
times, three observations were meaned (they were, by the way, usually identical), the 

* As AB was the thermometer immersed in the calorimeter it is with changes in its temperature 
tbat we have chiefly to do. 

t An error of '05 millim. in the setting of the bridge-wire contact-maker would correspond to a 
difference of -000455° at 40°, and the radiation, &c, due to such a difference would be negligible. The 
radiation, &c, coefficient of this calorimeter when full was about '00009 per 1° per sec, or the loss in 
temperature dne to a difference of 1° would be about "324° = 1004 thermal grams per hour (assuming 
the capacity as 310), thus a difference of - 01° throughout an experiment would have caused a loss or 
gain of 1 thermal gram. Of course, the differences in temperature rarely attained to "01°, and again, the 
differences were alternately + and — , so that the radiation, &c, loss or gain was evidently negligible. 
The radiation, &c, coefficient can be deduced from the experiments on the rate of rise made when 
determining the value of C'e L (Appendix II.). 

AIDCCCXCV. — A. 2 P 



290 MR. E. H. GRIFFITHS ON THE LATENT 

probable error was certainly less than 2. and, I believe, less than 1). Assume the 
probable error to be as great as 2, it follows that the differences of temperature 
could be determined to "0004°, and I am confident that differences of "0001° could 
be detected. 

There can be little doubt therefore that the quantity tq = C 9i { (9' — 6" ) + (d' — d")} 
could be determined to a far higher degree of accuracy than subsequent experience 
proved to be necessary. 

Note. — December 4, 1894. At Mr. Heycock's suggestion, I have to-day tested 
as follows the oil supplied to me by Mr. Thomas, and referred to in the preceding- 
section. We placed a lump of sodium in a test-tube filled with the oil, and gradually 
raised the temperature to above 160° C. No action whatever was visible, and the 
surface of the melted sodium remained as bright as that of pure mercury. We may 
assume, therefoi-e, that the manufacturers are justified in their statement that it 
consists of hydrocarbons only, and the probability that different samples would 
possess approximately the same composition is sufficient to make the determination 
of its specific heat of some value. 

Section VII. — The Heat due to the Stirring (Q,). 

I have already pointed out the necessity for rapid stirring. Throughout these 
experiments the stirrer revolved at a rate of about 310 to 320 revolutions per minute, 
which is a slow rate as compared with that adopted during my enquiry into the value 
of J. The conditions, however, are different. In my former work I had at times to 
make observations with the calorimeter only partially filled with liquid, and I found 
that unless the water was thrown over every part of the calorimeter, its capacity for 
heat varied with the depth of the liquid. Throughout my present work the calori- 
meter was full, the liquid almost touching the lid, and, in consequence, I considered 
the slower rate sufficient to ensure an even distribution of temperature. 

In my aniline experiments previously referred to, I eliminated the effect of the 
stirring-heat by finding the temperature (0 N ) at which the stirring supply exactly 
balanced the loss by radiation, &c, and thus the rate of rise at N enabled me to 
determine the effect of the electrical supply. As throughout my observations on 
latent heat I had to maintain the temperature of the calorimeter at an equality with 
the surrounding walls, this mode of elimination was not applicable. 

Two methods of finding the value of the mechanical supply suggested themselves. 

I. That of finding the mass of water which it was necessary to evaporate per hour 
in order to maintain the calorimeter at a constant temperature, when the supply of 
heat was that due to the stirring only. 

II. That of determining the rate of rise across the null-point (a) when the heat 
supply was that due to stirring only ; (b) when the heat was due to the stirring and 
a given potential difference. 



HEAT OF EVAPORATION OF WATER. 291 

I. I made a large number of determinations by this method, especially during the 
"preliminary experiments," of which an account is given in Section IX., where the 
evaporation was promoted by passing a current of dry gas through water. 

As I shall give details of the operations when describing the " preliminary experi- 
ments," I will not enter into particulars here, but I may now mention that the results 
by this method were by no means satisfactory, either as regards the determination of 
the stirring heat supply (Q^) or of the values of L. The discrepancies in the value of 
Q s are, however, not alone sufficient to explain the comparative failure of this method 
of finding L, for when both the rate and the temperature were the same, the varia- 
tions in Q s never attained to 1 in 20, and as Q, was but about one-hundredth of the 
total supply, the approximation was nearly sufficient. I omit any detailed account of 
these experiments, as I made no use of them in my final calculations, and it would 
needlessly fill much space. I will, however, give the conclusions they led to, as they 
corroborate the results obtained by the method finally adopted. 

Let 

in s = mass of water evaporated per 1 second by the stirring supply, 

and 

r = the rate of stirring (i.e., number of revolutions per second). 

When i diminished, the value of m, increased, and this rate of increase was much 
greater after the aniline was replaced by oil ; the change being evidently due to the 
increase of viscosity as the temperature diminished. When the stirring took place 
in aniline m, varied very nearly as r 3 , but Avhen oil was the liquid m, varied nearly 
as r*. 

In a former paper* I have proved that when the liquid was water the stirring heat 
varied almost exactly as r 3 , and I gave particulars of 108 experiments bearing out 
that conclusion. Again, in Paper A., I have shown that when using aniline with a 
different form of stirrer Q, oo r 2 approximately. Now with the same stirrer as that 
used in aniline we get with oil Q, oo r 4 ; at 50° the power of r should be slightly 
higher, at lower temperatures rather smaller. These differences, although surprising, 
are none the less real. 

In the case of water the conditions were so different (e.g., r was about 30 instead 
of about 5) that no comparisons could be drawn, but, in the case of the aniline and 
the oil, the conditions were almost identical. My incredulity with respect to the 
relations between Q, and r led to considerable delay, as I repeated these experiments 
unnecessarily, and it was not until a different method of observation led to the same 
conclusion that I felt any confidence in the results. 

II. I now pass to the method indicated in II. (supra), in which no weighings were 
involved, and where I was also able to dispense with the passage of air through the 
apparatus. 

* Paper J. 
2 P 2 



292 MR. E. H. GRIFFITHS ON THE LATENT 

Let t be the time of rising through a small range of temperature from below to 
above the surrounding temperature (6 ). 

If the heat supply is in one case due to both an electric current and the stirring, 
and in another to the stirring only, we have 

{d0 1 ldt) e ,-(d0 1 /dt) a =(dd 1 /dt) e (I.), 

where 0-, is the temperature of the calorimeter, and the suffix denotes the nature of 
the supply. 

And (using the notation on pp. 272 and 273) 

{d6Jdt), = QJC h , and (ddjdt), = Q,/C,„ 
therefore 

Q, (ddjdt), 



Q E " (ddjdt^ - (ddjdf), 



= f (II.)- 



Eq. (II.) will be true on any scale, and thus it is unnecessary to convert the 
bridge-wire readings into degrees C, and since 

Q.=/Q. (HI-). 

if e, n, and Rj be known, we can find Q„ for 

Q e = e 2 7i 3 /E 1 J (IV.). 

Thus Q s can be found, although the capacity for heat of the calorimeter and 
contents and also the scale of temperature are unknown. 

If we convert the bridge-wire degrees into C. degrees (N. thermometer) then, since 

{ddjdt) es - {ddjdt), = Q./C, 



we get 



Cei (ddjdi),, - (ddjdt), •■ • ( v -)> 

and thus C $l can be found. 

In Appendix I. I give particulars of the experiments by which the values of Q s for 
different values of 6 X were found. I regret that the observations are so few in 
number. Unfortunately I did not adopt this mode of experiment until the eleventh 
hour, and as these experiments were very lengthy, I should consequently have been 
unable to complete sufficient direct determinations of L to establish its value at the 
two points to which want of time compelled me to limit the investigation. 

On comparing the results with those obtained in oil by the previous method, 
I found that the agreement was sufficiently close to warrant a postponement of further 



HEAT OF ■ EVAPORATION OF WATER. 



293 



investigation on this point, and I am confident that the values of Q,, given in the 
following table are correct to better than 1 in 50, at temperatures 30° and 40°, although 
I am less certain about the values at 20° and 50° C.'" r The latter, however, are not 
required for the purposes of this paper, except in so far as they affect the specific heats 
of the oil in Table III. 

Table VI. — Thermal grams per sec. (Q s ) at rate (■»•) 5*300 revolutions per sec. 



V 


0.. 


r i - *• 


o 

50 

40 
30 
20 


•00235 
•00466 
•00665 
•00834 


298 x 10-8 

590 x 10-8 

843 x 10-8 

1056 x 10-s 



Let Q' s be the thermal grams per second due to a rate r v 
Then 

Q>i 4 = QsM = i, 

therefore 

Q',-0. = *(»-!* -»-*), 
therefore 

Q , t =Q 3 +k(r 1 i -r 4 ') 

Hence 

Temperature 40°, then Q', = -00466 + (r/ — 789) X "0000059. 

30°, „ Q', = -00665 + (r-* - 789) X '0000084. 



(1-) 



I do not, of course, suppose that Q s = hr* is the exact relation. I have already 
indicated that r 4 was too small at high, and too great at low temperatures. It must 
be remembered, however, that the variations in r were small, and thus the relation is 
sufficiently close for the correction of such variations as occurred during these 
experiments. 

If we assume that the work done (for a given value of r) is proportional to the 
viscosity, the values of Q, denote how great a change in viscosity is produced by 
raising the temperature from 20° to 50°. I repeat, however, that the values at 20° 
and 50° must be regarded with suspicion. 



* I have no corroborative experiment (by the former method) at 20°, and only one at 50° (see 
Appendix II.). 



294 MR. E. H. GRIFFITHS ON THE LATENT 

Section VIII. — Measurement of the Heat Developed by the Current (Q,,). 

A sketch of the electrical connections is given in Plate 6, fig. 3, and a full 
description will be found in Paper J., pp. 382-388, therefore I will here give only a 
brief description. 

Measurement of E. 

Leads marked 2 and 4 were connected with the storage cell circuit, leads 1 and 3 
with the Clark cells. A special form of rheochord was used consisting of two long 
barometer tubes (7 feet in length), which were so arranged that they could be raised 
or lowered by the rotation of handles ; thus the length of the vacuous space could 
be altered at will. Platinum wires passed down these tubes into the mercury. 
The wires were placed in parallel arc and thus one acted as a shunt to the other. 
The change in resistance depended, therefore, not only on the movement but on the 
ratio of the two resistances, and the instrument could be set so that a large move- 
ment caused but little change, or vice versa. The contact between platinum and 
mercury in vacuo was found to be very satisfactory. The resistance of the storage 
circuit could thus be altered at will. The Clark cell circuit contained a high 
resistance galvanometer Gj, with a resistance of about 9000 ohms, and joined the 
storage circuit at the roof of the calorimeter (at M and N, small sketch, Plate 6, 
fig. 3). By adjusting the rheochord the ratio of the external resistance of the 
storage circuit to the coil resistance could be altered at will, so that the D.P. at the 
ends of the coil became equal to that of the Clark cells, and the balance was 
maintained by watching the indications of G ls and, when necessary, adjusting the 
rheochord. The spot of light from G x passed down a tunnel 4 feet in length on to a 
sheet of ground-glass placed opposite the rheochord. In Paper J., p. 384, I have 
given the experimental numbers on which the following statement was based : — 

" It thus appears that the variations in E (the potential difference at the ends of 
the coil) were certainly within ToOToo °f the m ean value during the experiments, 
and changes in E, consequent on changes in the coil resistance, or the E.M.F. of 
the storages, could be disregarded." 

The effect of any error in determining E would be serious (the quantity E 3 being 
used in the reductions), and hence its accurate measurement was of great importance. 
I am satisfied, however, that (assuming the value of E for the Cavendish standard 
Clark cell to have been accurately determined) no error in the measurement of Q e is 
due to uncertainty as to the potential difference. The thirty-six Clark cells used 
have been fully described, in Paper J., pp. 385-388, as well as in the Paper by 
Messrs. Glazebrook and Skinner.* They have been compared with each other at 
regular intervals up to thepresent time, and their relative changes are small. At 
least three of these cells were always placed in parallel arc. Sometimes when 

* ' Phil. Trans.,' A, 1892, pp. 622-624. 



HEAT OF EVAPORATION OF WATER, 295 

•working with a D.P. of four ceils at least sixteen were really in use. Throughout 
these experiments they were maintained at a temperature close to 15° C, by a 
regulator which warmed the tank when below 15° C and turned tap-water through 
the tank when above 15° C. As full particulars are given in the pages of Paper J., 
I think the above summary will be sufficient. 

There is one alteration in the electrical connections to which I wish to draw 
attention. In former experiments some time always elapsed, after the current was 
established, before any observations were taken. It, however, appeared probable that 
in this woi'k I should occasionally have to cut off and put on the current during an 
experiment. For some time after the establishing of the current, a constant 
re-adjustment of the rheochord was required, as the temperature of the wires, &c, 
forming the external circuit was gradually raised, and the external resistance in 
consequence increased. During this period of adjustment the balance could not be 
as accurately maintained as when the temperature of the external wires had become 
steady. In order to avoid this preliminary adjustment, a coil of the same wire and 
resistance as that in the calorimeter was constructed and placed in a tube containing 
the same oil as that in the calorimeter, and this tube was fixed in the tank at F 
(Plate 6, fig. 3). 

At Jc x a key was so arranged that one movement brought the storages into 
connection with the calorimeter coil by means of leads 2 and 4, while another move- 
ment caused the current to leave the calorimeter circuit and pass through F. A 
second key (not shown in fig. 3) enabled the Clark cell to be also connected to F. 
The current was sent through F for 10 minutes or so and the balance adjusted, before 
an experiment commenced. On moving the key at \, the current was switched on 
to the calorimeter, the Clark cell circuit was then also shifted and the balance once 
more made perfect, Thus the current through the externals was kept constant 
whether it was passing through the calorimeter or not, and therefore the rheochord 
required far less manipulation. 

Again, the key h x was so arranged that whenever the current was shifted, a 
connection in a chronograph circuit was established, and thus the times of " making 
and breaking" the calorimetric current were automatically registered. True, the 
marked time was in each case a fraction of a second before the " make and break," but 
the actual duration of the intervals was truly recorded. 

Measurement of P^. 

The holes in the paraffin blocks P : and P 3 (Plate 6, fig. 3) contained mercury. 
Connection could be made by two cross pieces of copper rod, between either of the 
slots in P x and any of the holes in P 2 . These copper rods, when in position, rested on 
the wires which passed through the bottom of the holes. Denoting the resistance of 
the coil by P 1; that of the leads from P ?- to the lid of the calorimeter by r v r 2 , ?^ 3 , r±, 



296 



MR. E. H. GRIFFITHS ON THE LATENT 



it is evident that by a movement of the connecting rods, the following resistances 
could be taken, viz. : — 

r i + r 2> *i + R i + r s> r z + R i + r i, r -i + 'V 
If N l5 N 3 , N 3 , and N 4 , are the resulting numbers, we get 

E 1 ={(N 3 + N 3 )-(N 1 + N 4 )}/2, 

and there is no necessity that r v r 3 , r 3 , and r 4 should be equal. The value of R 1 was 
always obtained in the above manner, and then expressed in terms of the box ohm at 
17°. A full account is given in Paper J., pp. 407-410, of the comparisons of the 
individual coils of my resistance box with the B.A. Standards, and the values of R 4 
were reduced to true ohms in the manner there indicated, with the further corrections 
given in a later communication.""" 

In Appendix III. I give an example of an observation together with the reductions. 

It was next necessary to find the increase in R x (SR) due to the rise of temperature 
caused by the current. This was done in substantially the same manner as that 
described in Paper J., pp. 404-407 ; SR was in this case found to be very small — as 
shown by the following table. 

Table VII. 



Potential difference 

in terms of a 

Clark cell. 


oR. 


1 

2 
3 

4 


•00076 
•00198 
■00377 
•00630 



The resulting curve was (as in other similar cases) practically a parabola. 

A further correction was necessary for the heat developed in leads 2 and 4 in the 
portion that passed from the steel to the calorimeter lid. Their total resistance was 
"0068. We may assume that half the heat here generated passed into the calorimeter, 
and therefore consider their resistance as *0034 ohm = r. Now the points kept at a 
constant D.P. were between these wires and the coil, and since JH = E 2 /R (1 + ?'/R) ^ 
we get the effective resistance = R — r. 

The following table gives the values (after the application of all corrections) of R x 
at the temperatures at which the L experiments were performed, the potential dif- 
ference being denoted by the suffix. 

* ' Roy. Soc. Proc.,' vol. 55, p. 25. 



HEAT OF EVAPORATION OF WATER. 
Table VIIT. 



297 



Temp. 


R . 


R 3 «. 


R 3 «. 


R.i«- 


20 
30 
40. 

50 


10-3246 
10-3482 
10-3720 
10-3966 


10-3266 
10-3502 
10-3740 
10-3986 


10-3284 
10-3520 
10-3758 
10-4003 


10-3309 
10-3545 
10-3783 
10-4028 



SRj per 1° C. = -0024. 

This coil has shown no signs of any change throughout its history. 

As Q s = (ne) 3 /'R 1 J, I have now indicated how the value of Q e could be accurately 
ascertained. 

Had full details of the method not been given in previously published papers, it 
would have been necessary for me to give further particulars as to the various 
measurements. 

There can, I think, be little doubt that the value of Q e could be determined with 
great certainty. 

I have already (see p. 272 supra) pointed out that even if my value of J (4'199 X 10 7 ) 
be in error, it is the correct value to use for these experiments, and that even if e 
(the D.P. of a Clark cell) and the units in which R L is measured (i.e., the value of a 
" true obm ") are in error, the results are unaffected, provided that no changes have 
taken place in my Clark cells, or the coils of the resistance box since they were used 
for the determination of the value of J. 

[Note, May 4, 1895. — During the spring of this year my Clark cells were carefully 
re-compared with the Cavendish standard, R I. Comparisons were made at regular 
intervals, and Mr. Skinner was so kind as to take some independent observations. 
The differences are expressed in hundred-thousandths of the E.M.F. of the standard. 
The highest of the thirty cells exceeds R I by 40 such units. The lowest is less than 
R I by 36. The mean value of the whole set is less than R I by 3 such units (i.e., 
by "00004 volt). Thus, although the individual cells show larger discrepancies than 
in 1892-4, the mean value is almost exactly that of the Cavendish standard. The 
previous history of that standard shows that it had remained unchanged during the 
interval of eight years which had elapsed between the absolute determination of its 
E.M.F. by Lord Rayleigh in 1883, and that by Messrs. Glazebrook and Skinner 
in 1891. There is no reason to suppose that it has altered since the latter date, and 
this conclusion is borne out by comparison with other standards at the Cavendish 
Laboratory. I think, therefore, that I am justified in assuming that the mean E.M.F. 
of my cells remains practically unaltered. 

Cells 37 to 42 have been compared at Manchester by Professor Schuster with his 
standard. These six have the highest mean E.M.F. of any of my sets. Their mean 
value exceeds R I by 22 units, and they exceed Professor Schuster's standard by 

mdcccxcv.— a. 2 Q 



298 MR. E. H. GRIFFITHS ON THE LATENT 

70 units. It would thus appear that R I exceeds Professor Schuster's standard by 
48 units, i.e., by about 0'0007 volt. It must, however, be remembered that between 
these comparisons the cells had been subjected to several transits by railway.] 

Measurement of Time. 

The chronograph was controlled by the electric clock described in Paper J. (p. 414). 
The clock has remained untouched from July 1 6th to the present day — N ovember 1 8th, 
and during- that time it has gained 12 minutes, i.e., a gaining rate of about 1 in 15,000. 
The gain has been regular throughout the interval, the clock being singularly indifferent 
to small changes of temperature. I therefore consider that the measurements of time 
require no correction. 

Section IX. — The Results of Experiments in which Evaporation was 
Promoted by the Passage of a Gas. 

I have hitherto referred to the experiments I describe in this section as "pre- 
liminary " for want of a better name ; but I had originally hoped that the method 
would have given satisfactory results. Although these experiments have had but 
little influence on my conclusions, I will briefly describe them, as I am yet at a loss to 
account for their comparative irregularity. 

Dry air, or other gas, was forced in a continuous stream through the water to be 
evaporated ; the cooling thus caused was balanced as before described, and the weight 
of water evaporated determined by the increase in weight of drying bulbs. I wished 
to adopt this method, because by adjusting the flow of air the rate of loss of heat 
could be (by proper arrangements) regulated with nicety, and the thermal balance 
maintained with great accuracy. When water is made to boil by diminished pres- 
sure, the regulation of the cooling presents many manipulative difficulties that I was 
anxious to avoid. 

The experiments were conducted as follows. About 20 cub. centims. of water were 
placed in the flask F (Plate 6, fig. 1),* the water force-pump set going, and the air 
first passed through the H 2 S0 4 bottles and "tower" S, then through the U-tube 
and drying tower P — both containing P 2 5 . It then passed through the 3-way 
tap (T 2 ) into the 30-feet copper coil (Cj) in the tank water, thus attaining the tem- 
perature O of the tank, and after traversing the immersed tap T 3 , bubbled through 
the water in the silver flask. The air and vapour now rose up through the 18 feet of 
silver coil (C 2 ) within the calorimeter, passed out through the 4-way tap (T 4 ), which 
was opened in such a manner as to direct the air current into some HjSO^ bulbs (not 

* This figure is diagrammatic only, and conveys no idea of dimensions or actual position. For example, 
the coil Cj surrounded the steel vessel, and the 4-way tap T 4 was on the same side of the apparatus as 
the tap T 2 . The pipes, &c, crossed and re-crossed each other in such a manner as to render any direct 
representation impossible. The drying bulbs and connections are not indicated in the figure, as they 
were afterwards replaced by the condenser (B) and manometer (Mo). 



HEAT OF EVAPORATION OF WATER. 299 

shown in figure) containing the same depth of H 2 SOj, as the bulbs to be weighed. 
Thus when T 4 was afterwards so turned as to change the direction of the current to 
the weighing bulbs, no alteration took place in the rate of flow, which was adjusted as 
required in the following manner. A T-piece (not shown in sketch) was inserted in the 
tube between the drying tower P and the tap T 3 . The vertical leg of the T-piece was a 
wide graduated tube, open at its lower extremity, and immersed in a deep, narrow 
vessel (a hydrometer jar) filled with H 3 S0 4 . If the air pressure within the pipes was 
greater than that due to the column of H 2 S0 4 above the open end of this leg, the 
excess of gas bubbled up through the H^SO^ and escaped into the open air. Thus by 
raising or lowering the vessel the pressure and quantity of air passing through the 
whole apparatus could be regulated with exactness. I found it possible to so adjust 
the flow that when the heat supply was Q e and Q s> the galvanometer showed no 
change for nearly an hour. A further advantage of this arrangement was that I could 
close any tap without increasing the pressure within the apparatus, the whole of the 
gas then passing out through the regulator. The pressure of the gas near the flask 
was read on the manometer M l5 which had two wide bulbs near the base, the mercury 
filling the lower bend and three-quarters of the bulbs. The narrow tube on the scale 
side contained water resting on the mercury, and thus a very open scale was obtained. 
The instrument was carefully standardised, and a movement of 7 "7 8 centims. in the 
water level corresponded to a change in the pressure of 1 centim. of mercury. The 
water was completely cut off by the mercury from all communication with the gas 
tubes. 

The electric connections having been made and the rheochord adjusted until the 
high resistance galvanometer (G x ) showed that the D.P. at the ends of the coil was 
that of the Clark cells (I shall speak of this hereafter as the " electric balance," and 
of the adjustment of the loss or gain of heat as the " thermal balance "), the gas flow 
was then diminished until the platinum thermometer galvanometer showed that X 
slightly exceeded O (0 X = calorimeter temperature, O = temperature of surrounding 
walls). The current was then switched on to the alternative coil F (fig. 3), X now 
decreased and at the moment when 8 X = O the current was switched back again, 
the key itself recording the time on the chronograph tape. About the same time, 
the 4-way tap T i was turned so as to cause the escaping gas to pass through the 
weighing bulbs. This time had not to be recorded, nor was there any necessity that 
it should be nearly or at all coincident with the time of establishing the electric 
current. If, however, X did not exactly equal O at the moment of turning T 4 , the 
swing of the galvanometer was recorded and the tap only closed at the end of an 
experiment when the swing was identical with the initial one. 

When necessary the thermal balance was maintained for 1, 2, or, in some cases, 
3 hours by adjusting the flow of gas. At the close of an experiment X was again 
allowed to rise slightly above O , the current switched off" (again itself recording the 
time) and as 6 X descended the tap was turned back to its old position when 6 X = O , 

2 Q 2 



300 MR. E. H. GRIFFITHS ON THE LATENT 1 

or when the swing was the same as the initial one. The taps T 2 and Tj., were then 
turned so that the dry air instead of passing through the tank, &c, went straight 
through T 4 to the weighing bulbs, and thus any moisture left in the connecting tubes 
was swept into the bulbs. 

The swing of the galvanometer was rarely as much as 50 (indicating a difference of 
about 0°01 between 1 and 6 ) throughout one of these experiments, and when such 
oscdlations occurred care was taken to alter the adjustments so that a swing to the 
right was invariably followed by a similar swing to the left. The whole apparatus 
could easily be managed by two observers and, on occasions, it was unnecessary to 
make an alteration of any kind for half-an-hour at a time. 

As before stated, the stirrer automatically recorded on the chronograph tape the 
time of each 1000 revolutions. 

The weighing bulbs were of peculiar construction and specially designed for this 
work. The gas passed through four washings of H 2 S0 4 and then through a tube of 
P 2 5 , on the further side of which was attached a CaCl 2 tube. The latter was not 
included in the weighings, but only used to prevent any access of the laboratory air 
to the P 2 5 when the gas current was not passing. The weighing bulbs were 
connected with the exit tube by a mercury trap* and had simply to be lowered into 
place, no fitting of rubber tubes being necessary. To avoid condensation, the 
mercury trough and also the whole of the exit tube exterior to the tank were 
maintained at a temperature above O by means of small gas jets. 

At the close of an experiment the weighing-bulbs were removed (with their precisely 
similar tares) to the balance case. A careful weighing was made about an hour 
after the experiment, and again next morning ; an apparent increase of about '0005 
gram generally presenting itself. 

As (especially in the stirring experiments) small differences in weight had to be 
measured, I took every precaution I could devise, and I also followed the suggestions 
of friends whose experience in this matter was greater than my own. The balance 
was a short-beam one by Verbeck and Peckholdt, and was constructed so as to give 
a swing of 25 divisions per I milligram when loaded up to 500 grams. The actual 
weights to be measured were about 120 grams. I made special efforts to keep the 
temperature of the balance case steady, and noted the effects of changes in tempera- 
ture on the ratio of the arms, etc. 

The weights used were by Messrs. Oertling, and re-standardised by them last year. 

The increase in weight during the electrical experiments varied from "8 to 3*5 grams, 
the increase during the stirring experiments from - 06 to "08 gram. 

I think it certain that the weighing error was never so much as '002 gram, and it 
was probably much less ; thus I do not believe that any discrepancies in the values of 
L greater than 1 in 1000 can be due to errors of this description. 

As before described (p. 291) the mass of water evaporated by the stirring supply was 
* Neither bulbs noi- trough are shown in fig. 1, Plate 6. 



fiEAT OP EVAPORATION OF WATER. 



301 



determined in a similar manner. Thus, if m s be the mass evaporated per second by 
the stirrer, we have (using the same notation as before) 

ML - m s t s = Q e t e + tq. * 

I spent some weeks over these experiments, but the results were so uncertain, that 
at last I was compelled to give up all hopes of attaining my object by this method, 
I will therefore omit details and give results only. 



Table IX. — Evaporation Caused by Passing Dry Gas. 



Date. 



September 2 . 

2 . 

„ 11 . 

„ n . 
ii . 



August 29 
h 29 
„ 31 
„ 31 

September 



2 

2 

2 

12 

12 

13 



August 19 
19 
20 
22 
24 
24 
27 
27 
28. 



Number of 
Clark cells. 



2 
3 
1 
3 



Mean 



2 

1 
2 

1 
1 
2 
1 
3 
2 

2 



Mean 



Mean 



Temperature. 



49-54 
49-54 
500 L 
50-00 
50-00 



49-82 



39-98 
3997 
39-98 
39-98 
39-99 
39-99 
39-98 
40-0] 
40-00 
39-98 



39-99 



24-97 
24-96 
24-96 
24-96 
24-97 
24-97 
24-95 
24-95 
24-95 



24-96 



567-5 
564-4 
566-6 
566-3 

567-8 



566-5 



576-9 

572-2 
574-5 
572-9 
569-8 
572-9 
569-9 
572-2 
569-4 
572-7* 



572-4 



582-6 

580-6 

584-2 

581-7* 

580-0 

584-7 

581-5 

580-3 

581-4 



581-9 



Remarks. 



Calorimeter filled with aniline 



„ oil 



Calorimeter filled with aniline 



/Oil in calorimeter 
*Nitrogen passing 



*Nitrogeu passing 
)> Calorimeter filled with aniline 



* 2g in this case = (^{(e'o — 0" o ) + — d")} + C'», (T' — T") where C'», is the "mean mass" of 
the water in the flask, and T' and T'' the initial and final temperatures of that water as indicated by the 
flask thermometer G ? . 



302 MR. E. H. GRIFFITHS ON" THE LATENT 

I have included in the above table all the experiments with the exception of two, 
which were performed on the same day (September 3rd), and whose extreme diver- 
gence from the others led to the discovery that the insulation of one of the leads had 
fallen off. In consequence, the value of P^ was uncertain. Between September 3rd 
and 11th the whole apparatus was taken to pieces and fitted with new leads and 
insulators. From this time onwards the calorimeter was filled with oil in place 
of aniline (see Paper A., p. 77). 

I think it is evident that the discrepancies are greater than can be accounted for 
by errors in weighing, as they sometimes amount to nearly 1 per cent. 

I at first suspected that some moisture was escaping uncaught by the weighing 
bulbs, or that the entering air was not dry. I believe, for two reasons, that this was not 
the case. (1) The PX) 5 bulb, through which the gas finally passed, in no case iucreased 
in weight by as much as 0'0040 gram, and usually only by about 0'0020 gram, which 
showed how completely the moisture had been removed by the H 2 S0 4 . (2) Before 
entering the apparatus the gas passed also through H 2 S0 4 and P 3 5 , therefore any 
quantity of moisture which escaped these drying agents would be likely to also escape 
the similar agents at the exit- end, and thus would not affect their weight. I had 
good evidence that this was the case, for I thoroughly dried the flask and tubes at a 
temperature of 40°, and then passed the gas through the apparatus into the weighing- 
bulbs for an hour and a half; but the increase of weight in that time was not as much 
as "0005 gram. Again, if the gas was more completely dried at one end than at the 
other, the effect would have been to make all the values of L too low or too high. Of 
course, I was entirely in the dark at the time of these experiments as to the real 
value of L, but I now find that the mean of each group gives a close approximation 
to the true value, hence there was no permanent raising or lowering cause at work. 

It will be noticed that the rate of flow of air was greatly changed during these 
experiments ; when three cells were used the rate of evaporation had to be nine 
times as great as when the D.P. was that of one cell. Inspection of the table will 
show that the variations in the values of L do not appear to be functions of the rate. 

For some time I fancied that " priming " might be taking place, but, if so, the 
experiments with a rapid flow would probably all have given lower values than those 
with a slow flow, the carrying of particles of unevaporated water being much more 
probable when the velocity of the gas current was increased nine times. 

Again, it has been suggested that, as the pressure of the gas diminished during its 
passage through the apparatus, some heat would in consequence disappear. I would 
point out that the only constricted portions of the passage (after the air had once 
entered the tank) were within the calorimeter, and, if all the work done by the gas 
was performed within the calorimeter, the cooling, owing to expansion, would be just 
balanced by the warming of the tubes at the constricted points. Also, a persistent 
lowering of the values of L would be caused, and (as above pointed out) I now find 
that such is not the case. To test this matter at the time, however, I observed the 



HEAT OF EVAPORATION OP WATER. 



303 



rate of rise due to the " stirring supply " — firstly, when no air was passing ; secondly, 
when the air was passing through the dry flask and tubes and I could detect no 
difference. 

So lono- as the thermal balance is maintained with the same potential difference, 
the rate of evaporation must be the same, whatever method is adopted. I cannot 
see that the external work to be done is likely to alter because the space above the 
water is de-saturated by passing a gas instead of removing the saturated vapour by 
an exhaust, and this view is borne out by the close agreement between the means of 
those groups and my later experiments. 

There is one curious fact which may possibly throw some light on the matter. I 
performed two experiments (August 22 and September 13), passing nitrogen instead 
of air. Of course I had at that time no means of judging of the comparative value of 
the different experiments, and therefore was ignorant of the close approximation of 
the nitrogen values and my final ones. Had I then been aware of the coincidence, I 
should have continued the nitrogen experiments in order to ascertain if the agreement 
was fortuitous. 

The close agreement is shown in the following table : — 

Table X. 



Temperature. 


Results of nitrogen experiments. 


Pinal values. 


24 ? 96 
39 98 


581-68 (1 cell) 
572-72 (2 cells) 


581-73 
572-69 



When time allows, I propose to repeat these nitrogen experiments, in the hope 
that some light may thereby be thrown on the matter ; in the meantime, I am 
unable to suggest any sufficient explanation of this phenomenon. 

Section X. — The Method finally adopted. " Exhaust " Experiments. 



A study of the results obtained from the experiments described in the last section 
led me to the conclusion that it was necessary to seek some other method of 
attacking the problem. I have not described many of the precautions I gradually 
adopted during those experiments, but since none of them had produced any appre- 
ciable improvement it was evident that the real cause of the irregularities had not 
been ascertained. Even the entire change involved by the replacement of aniline by 
oil, the removal and refitting of the calorimeter, &c, appeared to have had no effect 
of any kind. 

I determined, therefore, to adopt an alternative method of producing evaporation, 
viz., by reducing the total pressure below the pressure of the saturated vapour. It 



304 MR. B. H. GRIFFITHS ON THE LATENT 

possessed the following great advantages : (1) there would be no necessity for the 
passage of gas through the apparatus, (2) the weighing-bulbs, &c, for catching the 
aqueous vapour could be dispensed with. I was, however, reluctant to adopt this 
method, for I anticipated that several practical difficulties would present themselves ; 
for example, it would be necessary to insert a known weight of water into the flask, 
and continue the experiments until the whole of that water was evaporated, thus I 
should not be able to finish the experiment at any time when 9 X = O , as was the case 
during the " pressure " experiments. 

It would also be more difficult to maintain the thermal balance at such perfection 
as in the former experiments, for it would be less easy to control the rate of 
evaporation. 

Again, when air was passing through the apparatus, the water in the flask was 
efficiently stirred and its temperature in consequence approximated closely to that of 
the calorimeter, even when the rate of evaporation was rapid. A thermometer (G 2 ) 
was, during the prelirninaiy experiments, placed as described in Section V., with its 
bulb near the bottom of the flask, and I found that the difference in temperature 
between the flask water and the calorimeter liquid did not, in the greatest case, exceed 
o, 15 C. If no gas was passing, the water would not be stirred, and it appeared 
probable that the difference in temperature might greatly exceed this amount. In 
this case not only would the observed temperature (6^) exceed the real temperature of 
the water, but also the vapour when escaping through the coil would abstract heat 
from the calorimeter, and thus (as pointed out by Winkelmann in his criticisms of 
Regnault's experiments) the resulting value of L would be too great. 

It did not appear possible to determine the interior flask temperature accurately by 
means of a mercury thermometer, whose bulb was placed in a chamber where the 
pressure was reduced to something between 10 and 100 millims., and if I placed a 
platinum thermometer in the flask, a third electrical circuit and galvanometer would 
have had to be added with a third observer to read the indications— additions which 
circumstances did not render possible. 

I did not feel that it would be of any use to adopt Regnault's method of 
determining the temperature by the vapour pressure (see Section II.), and I 
endeavoured therefore to find some means of preventing the temperature of the 
evaporating water from falling below that of the walls of the flask. 

It was evident that the smaller the quantity of contained water, the more nearly 
would its temperature approximate to that of the surface upon which it rested. If 
it was possible to discharge the water drop by drop on to the silver surface, the 
difference in temperature would probably be negligible, and after some trials I found 
a method of effecting this. A glass tube, exactly fitting into the communicating 
tube h h' (Plate 5, fig. 1) was closed at one end, the other end being drawn out so 
that it would pass through the constriction at the calorimeter lid (see p. 279), and the 
narrow tube which thus projected into the flask, terminated in a very fine opening. 



HEAT OF EVAPORATION OP WATEB, 305 

A tube of tliis kind (which I shall call a " dropper ") is shown in place in Plate 5, 
fig. 1. It was filled with water in the same manner as a "weight thermometer.'' 
To ascertain its action, I placed it within a wide glass tube whose lower end was 
closed. A constriction in the wide tube enabled me to stand the " dropper " within 
it, so that the narrow portion projected downwards (without touching the bottom) in 
the same manner as it would do when in situ above the flask. The upper end of the 
enclosing tube was connected with the exhaust pumps, a clamp being fixed on the 
connections. I found that when the pressure fell below that of the aqueous vapour, 
the water in the dropper was discharged into the surrounding chamber in a succession 
of small drops, but that if the communication with the exhaust was closed the 
dropping ceased. If the vacuum was maintained, the drops first thrown on the walls 
disappeared while a fresh supply was ejected. I concluded that when the space was 
absolutely saturated there was equilibrium, and I found that the disturbance of that 
equilibrium, caused by an almost imperceptible decrease in the pressure, was sufficient 
to maintain the flow. The size of the orifice of the dropper did not appear to be of 
any consequence, as I ascertained by experiment. Of course a certain amount of 
Avater- vapour must have been formed to saturate the space left within the dropping 
tube as the water retreated. It is evident, however, that the quantity thus evaporated 
would be very small. At the highest temperature at which I have yet worked (50° C), 
the specific volume of water- vapour is somewhat below 12,000, and as the volume of 
the droppers used did not exceed 4*1 cub, centims., the weight of water required to 
saturate this space would be about '001 gram, and at lower temperatures much less. 
The greater portion of the heat required for such evaporation must, however, have 
been taken from the calorimeter, for the shoulder of the dropper rested on the metal 
ring at the base of the tube h h' (Plate 5, fig. 1), and this ring formed a portion of the 
calorimeter. In order to make certain of this matter, I lowered the filled dropper 
into place, the contained water being slightly cooler than the calorimeter temperature, 
and deduced its water equivalent in the manner described in Appendix II., where I 
show how the capacity for heat of the thermometer (G 2 ) was ascertained. The weight 
of water and glass in the dropper being known, its water-equivalent could also be 
alternatively obtained by calculation. It was difficult to accurately ascertain the 
temperature of the dropper just before lowering it into place, but the experimental 
results were in practical agreement with the calculated ones, and heat which dis- 
appeared within the dropper must therefore have been taken from the calorimeter. 

It is thus evident that no correction is rendered necessary by this internal 
evaporation. 

The adoption of the exhaust method involved certain changes in the exterior 
connections. The weighing bulbs and mercury trap were replaced by the bottle B 
(Plate 6, fig. 1). The connecting tubes which passed into this bottle were ground to 
fit and no corks were used. The calorimeter exit tube did not dip into the H.,S0 4 
but terminated about an inch above the surface of the acid. The manometer gave 

MDCCCXCV. — A. 2 R 



306 MR. E. H. GRIFFITHS ON THE LATENT 

(after comparison with the barometer) the pressure of the vapour in the condenser. 
The tube H branched into two ; one was connected with a water pump, by which 
the pressure could be brought down to about 20 millims., and the other with a 
Geisslee's mercury pump. 

Description of an Experiment. 

The dropper was filled by alternate boiling and cooling,'"" and was allowed to stand 
m a vessel of warm water until the temperature had fallen to about 5° above that 
to which it was to be exposed during the experiment. After removal from the water 
it was thoroughly dried externally and placed in a short glass tube closed at both 
ends by rubber corks, a precisely similar tube closed in the same manner being used 
as a tare. The case and dropper when full weighed about 20 grams. 

The dropper was always filled some hours before an experiment and placed in the 
balance case until wanted. After the tank temperature had become steady the 
dropper and its case, having been weighed, were placed within a larger tube 
immersed in the tank water. 

The connections of the electric circuit having been completed, the calorimeter 
temperature (#]) was made coincident with the tank temperature (0 O ), the current 
being then switched on to the alternative coil, and thus (as previously explained) 
the temperature of the external resistances was kept steady, even when the current 
was not passing through the calorimeter. The dropper and case were then removed 
from the tank, a silk thread was joassed through a platinum loop, fused into the top 
of the dropper, and it was lowered into its place at the bottom of the tube h 
(Plate 5, fig. 1). The thread was withdrawn and an air-tight piston, consisting of a 
section of a rubber cork mounted on a glass rod, was thrust down h until it arrived 
at the top of the dropper. A slightly larger conical rubber cork, mounted on the 
same rod, closed the top of the tube h, therefore all diffusion or evaporation up the 
connecting tube was prevented, and no difficulty was experienced in closing it in 
such a manner as to be absolutely air-tight. 

It was necessary to delay the commencement of the experiment until the dropper 
and contained water had assumed the temperature of the calorimeter (6^). This 
took some time, although the temperature of the former must (owing to the previous 
immersion in the tank) have been very nearly 9 Y . Observation of the thermometer- 
galvanometer gave the extent of the cooling caused by the introduction of the 
dropping tube. The current was then switched on until 6 l again equalled Q , the 
galvanometer was observed, and the process repeated until no further cooling effect 
was visible. 

It appeared possible that slight evaporation through the fine opening of the dropper 
might during this interval be the cause of some cooling, and I was for a time very 

* I found that it was necessary to fix a small capillary tube within the dropper, otherwise the 
contained water refused to start boiling when the external pressure was removed. 



HEAT OE EVAPORATION OF WATER. 307 

uneasy about this point. I found, however, that if the tube, after filling and weighing, 
was placed in a desiccator for 12 hours with the opening uncovered, the loss of weight 
was less than O'OOS gram ; it was, therefore, not probable that any appreciable 
evaporation took place during the interval occupied by the temperature adjustment. 
Again, the dropper, after being filled, was removed from the beaker at a higher tem- 
perature than that of the tank, so that immersion in the caloi-imeter would not lead 
to the expulsion of any water, provided that the small air-bubble formed at the 
lower end when the dropper was cooled in the balance case did not rise into the 
upper part of the instrument, in which case the re-heating would possibly cause a 
small expulsion, owing to the warming of the air-bubble, which was previously absent 
from the tube. I think it just possible that this happened in some of the earlier 
experiments (Nos. I. to V.), but, after No. V., I adopted a new form of tube, of which 
the lower end was first turned up for about 1 centim., and then bent at right angles. 
Thus any air-bubble formed during the cooling remained at the open end, and also the 
water, when ultimately expelled, was thrown against the side of the flask (see Plate 5, 

fig- 1)- 

The results of experiments performed after this alteration are in closer agreement 

than preceding ones. 

When 9 X was found by observation to have become quite steady, the contact-maker 
of the bridge was carefully adjusted to the bridge null-point (see p. 288), and the 
swing (if any) of the galvanometer was read. If 9 1 was found to be lower than O , a 
further adjustment was made. In cases where 6 l slightly exceeded 6 , no adjustment 
was possible without again removing the dropper, so, unless the difference was 
considerable (e.g., a swing exceeding 50 or 60, that is, a difference of about O- 01 C, 
see Table V., supra), the experiment was proceeded with. Three observations were 
taken of the swing, and the chronograph tape was marked during the second observa- 
tion. This gave the commencement of the interval of time t„ i.e., the time during 
which the stirring supply had to be estimated. 

The pressure in the condenser B had been previously brought down below that 
required during the experiment, and, immediately after the observer at the gal- 
vanometer had registered the swings, the tap T 4 was opened. The manometer M at 
once showed an increase of pressure, d ue to the air in the flask and tubes expanding 
into the condeDser. The expansion of this air produced a visible cooling effect, 
causing a galvanometer swing of about 90 — equivalent to nearly O- 02 C. (Table V., 
supra). The manner in which this loss of heat was compensated for will be described 
later. 

The water pump having been cut off by the tap T 6 , the mercury pump was if 
necessary brought into action. The moment at which the discharge from the dropper 
commenced was indicated with great accuracy by the galvanometer and announced 
by Observer No. II. The electric current was at once switched on to the calorimeter 
circuit (the action recording itself on the chronograph tape) and the electric balance, 

2 E 2 



308 MR. E. H. GRIFFITHS ON THE LATENT 

if not perfect, immediately adjusted by Observer No. I. Owing to the alternative- 
circuit method previously described, only a very trifling adjustment was as a rule 
required. Observer I. had now to direct his attention to the maintenance of the 
thermal balance. This, as I have anticipated, was found at first to be matter of some 
difficulty, but practice rendered the task comparatively easy. 

The discrepancies observable in the earlier experiments (Table XL) are, I expect, 
in some measure due to fluctuations in the value of V As a general rule, the 
evaporation at the start was too rapid, the pressure having been too much reduced 
by the last stroke of the pump — the galvanometer swing amounting to as much as 
— 500 or — 600 (nearly 0°'l O). The tap T 4 was closed and (evaporation being 
thus prevented) the electric current was allowed to raise 1 until the + galvanometer 
swing announced by Observer II. was about equal to the previous negative swing ; 
the time occupied by these two large oscillations being only a minute or two. T 4 
was then partially opened until it was found that X was slowly falling. When 0± 
became equal to O the rate of cooling was further decreased and during the remainder 
of the experiment the galvanometer swing (which was called aloud by Observer II. 
every 15 or 20 seconds) rarely exceeded 50 or 60 (i.e., about O- 01 C.) and in many 
cases the difference between 1 and O did not exceed o- 002 C. in the course of half- 
an-hour. 

As the whole of the aqueous vapour passing into the condenser was not at once 
absorbed by the H 3 S0 4 , the pressure slowly increased, and thus gave a further power 
of adjustment. The large bulb of the Geissler was kept vacuous and thus, by 
opening the tap T 7 the pressure in the condenser could at any time be decreased. 
By one rapid turn of the tap an almost imperceptible rise of the manometer M was 
caused, and a very slight difference in pressure produced a considerable alteration in 
the cooling rate ; thus, if X was rising, a single revolution of the tap T 7 would check 
the rise, another revolution would probably give the cooling a slight mastery. The 
operations by which the thermal balance was maintained may, as I have described 
them, appear both cumbersome and difficult. I can only say that (after the first 
three or four experiments) the control was nearly perfect and a single oscillation of 
as much as 0°"01 C. would have been considered excessive. From beginning to end 
of each experiment great care was taken that each positive oscillation should be 
succeeded by a corresponding negative one. 

The electric balance was also maintained by Observer I. ; but as the temperature 
of the coil did not appreciably alter throughout, this balance required but little 
attention. 

The taps T i; T 6 , T 7 , and T 2 ,as well as the handles of the rheochord and all the 
electric keys, were so placed as to be within reach of Observer I. without change of 
position. The high resistance galvanometer screen was immediately in front of him, 
and also the manometer, M, whose readings were constantly observed. Near the 
commencement and end of an experiment the physical strain was great, but when both 



HEAT OF EVAPORATION OF WATER. 309 

thennal and electrical balances had been finally adjusted there were often intervals of 
more than ten minutes when no alterations had to be made. 

From beginning to end, the task of Observer II. was that of announcing the 
galvanometer swings — a monotonous and uninteresting operation, which, however, 
required constant attention. 

When the experiment was approaching its termination a close watch had to be kept, 
for, unless the current was switched off the instant a sudden rise showed that all the 
water had been evaporated, the lapse of a few seconds would have raised X consider- 
ably above O . If, on the other hand, the current was turned off too soon, it was 
always possible to switch it on again and raise X up to O . After the first 
experiment it was easy to calculate (knowing the weight of the empty and the full 
dropper) the approximate time of ending. As a rule I cut off the current two or three 
seconds before that time, then increased the vacuum considerably to make sure 
of evaporating off the last drop of water, again established the current, and brought 
0j to just below O , repeating this process as often as necessary — all the actions 
recording themselves on the chronograph tape. When 9 l had become absolutely 
steady, or only showed the slight increase due to the stirring, it was safe to assume 
that all the water had been evaporated. 

The tap T 4 was then finally closed, the tap T 3 slowly opened, and the air from the 
drying bottles S and P allowed to pass in through the 30-feet coil, C lf in the tank. The 
increase of 1 caused by the compression of this air was found, by observation, to be 
the same as the depression (previously referred to) which took place during exhaustion) 
and it was to allow for this rise that Y was set slightly below O . When the internal 
and external pressures had become equal, T 3 was closed and the current again switched 
on if necessary, until the swing became the same as the initial swings. If, however, } 
exceeded O , this was not possible, and a correction had afterwards to be made for any 
difference. 

After repeated observation had shown that l was steady, Observer II. read, as 
before, three galvanometer swings, pressing his chronograph key at the middle one. 
This record gave the termination of the interval t e , the time during which the stirring 
heat had to be estimated. 

It will be seen from the preceding account that t, always considerably exceeded t e , 
the time of electrical supply. 

The plugs closing the tube h h' (Plate 5, fig. 1) were now withdrawn, a wire ending 
in a hook passed down the tube, the dropper extracted by means of its platinum loop, 
and immediately returned to its case, which was at once corked and placed on the 
balance, and afterwards weighed, with the various precautions previously referred to. 

The only remaining operation was that of translating the chronograph tape which 
gave the value to yg- second of t„ t e , and the time of each thousand revolutions of 
the stirrer. 

Remarks on Tables XI. to XIII. 

Tables XL, XII., and XIII. give the experimental results ; Table XL those at 



310 MR. B. H. GRIFFITHS ON THE LATENT 

temperatures approximating to 40° ; Table XII. those at temperatures near to 30° ; 
and Table XIII. two experiments at 30°, where the rate of evaporation was but T -g of 
the former rate. Any inaccuracy in the values of Q a , t s , and %q would in these last 
experiments tell with double force. Also, the rate of evaporation being so greatly 
diminished, it was probable that any depression of the temperature of the evaporating 
water below 6 l would be about balf of what it was when four cells were used, and 
thus the magnitude of any error, caused by such depression, would be indicated. 

Had time permitted, I should have repeated these experiments with a still slower 
rate of evaporation. I was, however, surprised to find that it was more difficult to 
maintain the thermal balance with the lower than with the higher D.P. 

A large number of differently shaped and sized " droppers " were used, hence the 
difference in the values of M. . 

As I preferred to alter the conditions as much as possible, no effort was made to 
keep the stirring rate the same for different experiments. 

In most cases the droppers when removed after an experiment appeared to be 
absolutely dry. In two cases, however, some signs of moisture were visible. I am 
at a loss to account for this, as I feel sure that evaporation had ceased, and that 
there was no water left on the surface of the silver flask. The moisture thus 
remaining was, of course, included in the final weighing, and would not therefore 
introduce any error provided the flask was dry. It is noticeable, however, that the 
two experiments at the end of which this moisture was visible (Nos. V. and IV.) 
give, as shown by Table XL (6), the highest values for L. # 

The value of d' — d" will be noticed as unusually high in No. I. Here we had no 
idea of the time when the experiment would finish, and did not allow for the rise in 
1 caused by the introduction of the dry air at the end, hence the close of the experi- 
ment found 0] too high by nearly 0°'028 C. Also we could only approximate to the 
value of t s , having in the hurry of the initial experiment forgotten to mark the time 
of finish. The remembrance of a casual observation of the clock, however, enabled us 
to fix it approximately. An error of 100 seconds in t„ would in that experiment 
produce an error of not quite ± - 25 in L, and the value assigned to t, is probably 
within a minute of the truth. 

During Experiment II. a portion of the mercury covering the core of tap T 3 became, 
owing to careless manipulation, sucked into the apparatus, and in some unexplained 
manner stopped the evaporation for nearly ten minutes, during which the electric 
current had to be switched off. However, the accident had but little effect on the 
resulting value of L. 

No. XL was an almost perfect experiment, the thermal balance being maintained 
very closely throughout. I do not think that the variations in 6 X during this experi- 
ment at any time amounted to O- 005 C, and the external temperature (6 Q ) remained, 

* Even when the same dropper was used, and the bulb was afterwards found to be dry, the values of 
M were not identical. The mass of contained water depended on the temperature of the dropper when 
removed from the beaker after filling, and as the beaker was only roughly brought to a temperature 
somewhat above 6 r , the values of M varied. 



HEAT OF EVAPORATION OP WATER, 311 

as shown by Col. III., absolutely unchanged. It is noticeable that its result 
(Table XI. (&)) is almost exactly the mean value of Experiments VI. to XII. 

I have included in these tables every experiment performed by the exhaust method 
with the exception of one, during a portion of which the chronograph ceased to mark, 
or rather marked continuously. Both accident and its cause were only discovered at 
the end of the experiment, when it was found that a loose piece of wire had short- 
circuited the chronograph circuit. 

Notation used in Tables XI. to XIII. 

Col. I. Number of experiment and date. 

„ II. Temperature of the experiment (0 O ) on the nitrogen scale. 

,, III. m i the initial mass of dropper and contents, m x the final mass ; hence 
m 1 — m 2 = mass evaporated = M. 

(M is in all ca.ses the weight corrected to vacuo.) 

„ IV. Time (in seconds) during which the electric current was passing through 
the calorimeter = t e . 

,, V. Time t s (in seconds) during which the stirring supply of heat was main- 

tained. t s = duration of experiment. 

,, VI. Number of revolutions per second of the stirrer = r v 

,, VII. Difference (9' — 6" ) between the initial (6' ) and final (6" ) temperature 
of the surrounding walls. This is expressed in the nitrogen scale, the 
value of each millimetre of thermometer II. having been previously 
determined by the comparison referred to in Section IV. 

,, VIII. Let 6\ (initial calorimeter temperature) exceed 6' by d", and let &\ (final 
calorimeter temperature) exceed 6" by d" . 
Then this column gives value of d' — d" deduced from the galvanometer 
swings by Table V., Section VI. 

,, IX. Gives the capacity for heat of calorimeter and contents (C S J at the tem- 
perature of the calorimeter Q x (Table III.). 

,, X. The temperature of the Clark cells during the experiment. 

,, XL The value of Rj at temperature 6 Y from Table VII., Section VIII. 

,, XII. The average pressure {p") in the condenser during the experiment (in 
millimetres of Hg). 

„ XIII. The approximate pressure of saturated vapour (p) at the temperature 1 
(from Regnault's tables). 

„ XIV. The difference between Cols. XIII. and XII. This indicates the limit of 
fall of pressure from the flask to the condenser, i.e., along about 
19 feet of narrow tubing. It must be remembered that owing to the 
presence of the H c S0 1 the pressure in the condenser fell off greatly, 
and Col. XIII. is only useful as indicating a value considerably 
exceeding the real difference between p and p". No use is made of 
this quantity in the reduction of the observations. 



312 



MR. E. H. GRIFFITHS ON THE LATENT 



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314 MR. E. H. GRIFFITHS ON THE LATENT 

Reduction of the Observations given in Tables XL (a) to XIII. (a). 
(See Tables XII. (b) to XIII. (6).) 

Col. XV. gives the value of Q e t e = — =^ • 

Rj X J 

The correction for temperature of the cells was made by Lord Rayleigh's coefficient 
(•00077), but, as an inspection of Col. X. (supra) will show, the correction was in 
every case very small, except in XL During the night of September 25 the Clark 
cell tank regulator ceased to work, and I found the cells at a temperature of 13°'8 the 
next morning. I considered it better to keep them at that temperature throughout 
the day than to raise it to 15° a few hours before an experiment. The correction in 
this case amounts to 1 in 1500, but is probably accurate to 1 in 5000. 

In a communication to the Royal Society, on November 22, 1894, Professor Schuster 
pointed out an error in my determination of the value of J, viz., that I had not made 
a necessary correction for the specific heat of the air displaced by the water, for the 
method I adopted gave the difference in the rate of rise when a certain space was 
filled first with air and then with water. This correction raises my value of J by 
1 in 4000. Hence, in the following reductions I assume J=4'199 in place of 4'198.* 
As I have before pointed out, if in consequence of errors in my standards, &c, my 
value of J is inaccurate, it is still the right value to insert here, where I use the same 
standards, for errors of the kind referred to are thus eliminated. 

Col. XVI. The value of Q, as deduced from Col. VI. by means of Table VI., 
Section VII. (supra). 
„ XVII. The " stirring supply " Q s t s from Cols. XVI. and V. 
„ XVIII. The term tq = C,, {(0' o - 6" ) - (d' - d")} from Cols. VII., VIII, and 
IX. 
XIX. Gives the sum of Cols. XV, XVIL, and XVIIL, that is, the total 
number of thermal grams used in evaporating the mass M (Col. III.). 
,, XX. Repeats the value of 6 Q , in order to render the reference less trouble- 

some. 

,, XXI. The value of L, deduced from the equation L = — '- rjr 1 — • 



* This correction should not be applied to the values of the specific heat of aniline given in Paper A. 
In that case the results also depended on the observations of differences, and if the corrected value of J 
was there used, a further correction for the specific heat of the air displaced by the aniline would have 
to be made, the final values remaining practically unaltered. 



HEAT OF EVAPORATION OP WATER. 



315 



Table XI. (b). — Eeduction of the Observations in Table XI. (a), (n = 4.) 





XV. 


XVI. 


XVII. 


XVIII. 


XIX. 


XX. 


XXI. 


Experiment. 


QeU 


Q s - 


QA. 


2g. 


2. 


O . 


L. 


I. 


21640 


■00443 


14-3 


-8-8 


2169-5 


40 ? 147 


57311 


II. 


2152-1 


•00454 


18-5 


+ 1-7 


2172-3 


40-146 


572-31 


III. 


1987-3 


•00509 


19-4 


+ 0-2 


2006-9 


40147 


572-77 


rv. 


1999-5 


•00449 


16-8 


+ 1-8 


2018-1 


40-144 


572-61 


v. 


2000-9 


•00471 


16-6 


+ 3-4 


2020-9 


40-145 


573-80 


VI. 


2189-1 


•00486 


23-8 


-3-4 


2209-5 


40-147 


573-01 


VII. 


2133-4 


•00546 


20-3 


+ 3-3 


21570 


40-147 


572-50 


VIII. 


21910 


•00480 


191 


-0-4 


2209-7 


40-147 


573-00 


IX. 


2271-7 


•00452 


20-3 


-o-i 


2291-9 


40-149 


572-28 


X. 


2269-7 


•00517 


22-7 


+ 1-1 


2293-5 


40-157 


572-12 


XI. 


22736 


•00468 


193 


-0-2 


2292-7 


40-133 


572-61 








Mean of 
Mean of 


all 


40-146 


572-74 




Nos. VI. to XL . . . 


40-147 


572-59 



Table XII. (b). — Reduction of the Observations in Table XII. (a), (n = 4.) 



Experiment. 


XV. 


XVI. XVII. 


XVIII. 
2$. 


XIX. 

2. 


XX. 

e . 


XXI. 
L. 


XII. 

xni. 

XIV. 

XV. 

XVI. 


2288-5 
2277-2 
2276-9 
2279-3 
2400-1 


•00672 30-4 
•00723 316 
•00710 32-1 
•00663 307 
■00614 30-7 


-3-8 
-0-5 
-1-3 
+ 0-9 
+ 0-2 


23151 

2308-3 
2307-7 
2310-9 
2431-0 


29 ? 987 
29-983 
29-998 
29-999 
30-004 


578-58 

578-64 
578-78 
578-90 
578-60 


Mean .... 


29-994 


578-70 



Table XIII. (b).— Eeduction of the Observations in Table XIII. (a), (n = 3.) 



XV 

Experiment. \ n , ' 


XVI. 


XVII. 


XVIII. 
2 3 . 


XIX. 

2. 


XX. 

e . 


XXI. 
L. 


XVII. 
XVIII. 


1750-1 
1753-4 


•00644 
•00696 


36-7 
36 7 


-o-i 

-1-7 


1786-7 
1788-4 


29 ? 993 
29-993 


578-83 
578-60 


Mean .... 


29-993 


578-72 



2 s 2 



316 MR, B. H. GRIFFITHS ON THE LATENT 

I have already remarked that I attach more value to Experiments VI. to XI. than 
to the preceding ones, and I shall therefore assume the mean value of L at 40 o- 15 as 
572-60. 

The close agreement between the means of Nos. XII. to XVI. and Nos. XVII. 
and XVIII. is very satisfactory when it is remembered that the rate of evaporation 
is in the last case nearly halved. 

I need scarcely say that, had time permitted, I should have performed more experi- 
ments, especially at 30°. I do not, however, consider that the evidence would have 
been greatly strengthened. 

In the whole of the series from VI. onwards (i.e., after the adoption of the bent 
form of dropper) there is no experiment which gives results differing from the mean 
at that temperature by more than 1 in 1430, and in the groups at 30° the greatest 
divergence is 1 in 2900. The probable mean error of a small group of experimental 
results of this kind is therefore less thaD the probable error of some of the constants 
on which our conclusions are based, and a larger accumulation of such experimental 
numbers would not necessarily bring us any nearer to the absolute value. 

Conclusions. 

Temperature. Value of L 

Nitrogen thermometer. (in terms of thermal unit at 15° C). 

40°-15 C. . 572-60 

30°-00 C 578-70 

Section XL — Discussion of the Results. 

From the conclusions arrived at in the last section we obtain (over the range 
30° to 40°-15 C.) dLjdd = -6010. 

Suppose we assume with Regnault that L is a linear function of 6, it follows that 

when (9=0°, L = 59673 
„ 6= 100°, L= 536-63 

I admit the folly of attempting to extrapolate to such an extent where we have no 
evidence but that given by the experiments themselves. It is a different matter 
when we can bring forward independent evidence. 

In Section II. I dwelt upon the importance of the experiments of Dieteuici at low, 
and of Regnault at high temperatures ; the agreement between the values obtained 
by those observers and the ones resulting from the above extrapolation is so extra- 
ordinary that I give in detail their experimental numbers. 

As stated in Table I., ante, the mean value of all Dieterici's experiments was 
596'8 at 0°. He, however, regards certain of the experiments (whose results are 
given in his Tables II. and IV.) as of greater value than others, because the 
evaporating water was included in a platinum instead of a glass tube, and thus its 



HEAT OF EVAPORATION OF WATER. 



317 



tempei*ature must have approximated more nearly to the external temperature. His 
numbers are as follows (' Wied. Ann.,' vol. 37, 1889, pp. 502-4) : — 

Table XIV. — Dieterici's Experiments. 

597-29 
597-19 

595-99 

< 596-'?6 
595-74 
596-51 
597-06 



Table IV. 



j 597-07 (with lower pressure) 
• \ 596-68 



Mean of all experiments "1 » q R . no 
in platinum tubes . . J 

His own summary of these results is as follows : — 
" Die Versuche mit dem Platingefasse ergeben 

r= 59673 

mit einem wahrscheinlichen Fehler des Mittels von ± 0*13."* 

PtEGXAULT performed forty-four experiments at temperatures about 100°, Of 
these he rejects Nos. 1 to 6, as merely preliminary ; the remainder are as follows. It 
should be remembered that the numbers in this table give the values of the " total 
heat," not those of L. 

Table XV. — Kegnault's Experiments. 



Experiment. 


Temperature. 


"Total heat." 


Experiment. 


Temperature. 


" Total heat." 


7 


99-49 


636-8 


26 




100-22 


6372 


8 


99-46 


6363 


27 


100-37 


6361 


9 


99-31 


6364 


28 


100-32 


636-1 


10 


99-28 


6376 


29 


100-32 


637-3 


11 


100-19 


636-0 


30 


100-31 


6361 


12 


10019 


636-8 


31 


100-22 


635-6 


13 


100T9 


638-3 


32 


100-22 


636-9 


14 


100-19 


637-9 


33 


10026 


635-9 


15 


100-19 


635-9 


34 


100-26 


635-9 


16 


100-26 


635-9 


35 


9909 


635-7 


17 


100-26 


637-9 


36 


99-09 


636-1 


18 


100-26 


6379 


37 


99-07 


636-6 


19 


100-26 


635-6 


38 


99-07 


636-9 


20 


100-26 


635-8 


39 


99-36 


636 1 


21 


100-26 


636-7 


40 


99-36 


636-8 


22 


100-22 


637-6 


41 


99-33 


637-3 


23 


100-22 


638-4 


42 


99-33 


636-4 


24 


100-22 


636-8 


43 


99-27 


635-7 


25 


100-22 


636-6 


44 
Mean . . 


99-27 


636-S 


99-88 


636-67 



* ' Wied. Ann.,' vol. 37, 1889, p. 504. 



318 



MR. E. H. GRIFFITHS ON THE LATENT 



This value of 636-67 at 99°-88 would become 636-60 at 100°. If we assume that 
1 gram of water gives out 100 thermal units in cooling from 100° to 0°, we get 

L = 536-60 at 100°. 
Values of L. 



Regnault 

Griffiths (extrapolated) . . 


0°. 


100°. 


596-73 
596-73 


536-60 
536 ; 63 



I have learned to regard experimental coincidences with suspicion, they are so 
often misleading, but such an unusual case as the above merits attention. 

These coincidences are the more extraordinary on account of the following con- 
siderations. 

Dieterici assumed (ante, p. 265) as his thermal unit the "mean thermal unit" 
from 0° to 100° C. Now according to Regnault* the ratio of the "mean thermal 
unit" to the thermal unit at 0° is as 1'005 to 1. 

If we assume Rowland's or Bartoli and Steacciati's determinations of the 
changes below 15° (my own have not extended below that temperature) we should 
get 

" mean thermal unit " l - 005 . . 

"thermal unit at 15°" = ^994 ^proximately, 



■i.e., — - - and thus Dieterici's value of L, if expressed in terms of the same thermal 

unit as I have used, would be increased to 6 03 "3. 

Again, according to Regnault we ought to subtract 100'5 from 636*60 in order to 
obtain the value of L at 100. This would o-ive L = 536'1. 

Some further considerations, however, tend to show that the agreement at both 
ends of the line given by my observations is not merely fortuitous. We can deduce 
the values of L resulting from my " exhaust" experiments (at any temperature 6) by 
the formula, 

L = 596-73 - -6010 6 . . . (G^. 

Now the preliminary experiments (see Table IX., ante) although irregular, carry 
some weight and the mean of each group is in fair agreement with formula (G x ). 

* " De la Chaleur Specifique," 'Menioires de l'Academie des Sciences,' tome 21. 



HEAT 


OF EVAPORATION 

Table XVI. 


OF WATER. 


Temperature. 


L from " preliminary " 
observations 
(Table IX.) 


L from formula G v 


25-0 
40-0 
49-8 


581-9 

572-4 
566-5 


581-70 
572-69 
566-80 



319 



I have given in Section II. my reasons for rejecting Regnault's experiments at 
low temperatures, where he determined the temperature in the calorimeter from the 
pressure of the vapour in the condenser. The objections there brought forward, 
however, lost all force as regards these experiments above 63° in which the methods 
of observation and experiment were altered. 

Column III. of the following table give3 the results of all Regnault's experiments 
above 63° aud below 100° . . . (R e ), Column IV. gives the values resulting from 
Regnatjlt's own formula 606"5 + "305i .... (R), Column V. contains those given 
by Winkelmann's formula* . . (W), which includes Regnatjlt's expression for 
the capacity for heat of water, and Column VI. the numbers obtained by assuming 
the validity of formula G, (supra), from which we deduce 

Total Heat = 59G73 + -39900 .... (G 2 ). 

Column VII. gives the difference between (R e ) and (R), in Column VIII. are given 
the differences between (R t .) and (W), and Column IX. shows the differences between 
(R,) and (G 2 ). 



* L = 589-5 - 0-2972* - 0-0032147;! 3 + 0000008147i« 



320 



MR. E. H. GRIFFITHS ON THE LATENT 



Table XVII. — Comparison between Regnault's Experimental Results (R P ) over the 
Range 63° to 88°, with the value given by formula? (R), (W), and (G 2 ). 



I. 


II. 


III. 


IV. 


V. 


VI. 


VII. 


VIII. 


IX. 


No 




Experi- 














of experi- 
ment. 


Tempera- 
ture. 


mental 

results. 

(R f .) 


(R.) 


(W.) 


(&,) 


(R,)-(R). 


(R,)-(W). 


(R e )-(G 2 ). 


1 


88-11 


633-4 


633-4 


632-4 


631-9 





+ 0-9 


+ T5 


2 


87-83 


6331 


633-2 


632-3 


631-8 


- o-i 


+ 0-8 


+ 1-3 


3 


85-97 


628-4 


632-7 


631-7 


6310 


- 4-3 


- 3-3 


-26 


4 


85-24 


628-6 


632-5 


6315 


630-7 


- 39 


- 2-9 


-21 


5 


85-20 


631-7 


6325 


631-5 


630-7 


- 0-8 


+ 0-2 


+ 1-0 


6 


84-68 


629-9 


632-3 


631-2 


6305 


- 2-4 


- 1-3 


-0-6 


7 


83-08 


628-9 


631-8 


630-7 


629-9 


- 2-9 


- 1-8 


-1-0 


8 


82-66 


631-0 


631-7 


630-6 


629-7 


- 0-7 


+ 0-4 


+ 1-3 


9 


81-03 


628-8 


631-2 


630-0 


629-1 


- 2-4 


- 1-2 


-0-3 


10 


80-60 


627-7 


631-1 


629-9 


628-9 


- 3-4 


- 2-2 


-1-2 


11 


80-37 


628-8 


631-0 


629-8 


628-8 


- 2-2 


- 1-0 





12 


80-17 


630-2 


630-9 


629-7 


628-7 


- 0-7 


+ 0-5 


+ 1-5 


13 


79-55 


630-1 


630-8 


629-5 


628-5 


- 0-7 


+ 0-7 


+ 1-6 


14 


78-28 


627-0 


630-3 


629-0 


628-0 


- 3-3 


- 2-0 


-10 


15 


76-50 


628-6 


629-8 


628-3 


627-2 


- 1-2 


+ 0-3 


+ 1-4 


16 


71-35 


624-4 


628-2 


626-4 


625-2 


- 3-8 


- 2-0 


-0-8 


17 


71-11 


622-2 


628-1 


626-3 


625-1 


- 5-9 


- 4-1 


-2-9 


18 


70-49 


626-9 


628-0 


626 1 


624-9 


- 1-1 


+ 0-8 


+ 2-0 


19 


69-70 


626-4 


627-7 


6257 


624-5 


- 1-3 


+ 0-7 


+ 1-9 


20 


68-01 


622-5 


627-3 


6251 


6239 


- 4-8 


- 2-6 


-1-4 


21 


66-30 


6247 


626-7 


624-5 


623-2 


- 2-0 


+ 0-2 


+ 1-5 


22 


64-34 


622-9 


626-1 


6239 


6224 


- 3-2 


- 10 


+ 0-5 


23 


63-02 


625-5 


625-7 


623-2 


621-9 


- 0-2 


-f- 2-3 


+ 3-6 






Sum of differences 






-49-3 


-17-6 


+ 5-2 






Mean d 


ifFeren.ee . 


- 2-14 


- 0-77 


+ 0-23 








I 


f we omit I 


Experiment 23, we get 
















Sum of differences 






-49-1 


-19-9 


+ 1-6 


Mean c 




- 2-23 


- 0-90 


+ 0-07 









The results of the above comparison show that over the range 63° to 88° the 
formula (G 3 ) gives a closer approximation to Regxault's experimental numbers than 
either of the other formulas. 

The only reasonable explanation of these various coincidences which occurs to me is 
that the value of the "mean thermal unit " is practically the same as the value of the 
"thermal unit at 15° C."* 

* Further evidence can be adduced in support of this view. In Section II. I pointed out that if we 
express the results of the observations of Buxsen and Regnat:lt, on the latent beat of fusion of 



HEAT OF EVAPORATION OP WATER. 321 

I see nothing impossible in this supposition. As stated in Section II. there is 
sufficient evidence that at low temperatures the capacity for heat decreases with rise 
of temperature. Rowland found a minimum indicated near 34°. If therefore the 
capacity for heat increases gradually above some such temperature, but more rapidly 
near 100°, it is quite conceivable that the "mean thermal unit" should closely 
approximate to the "thermal unit at 15° C" Our only experimental evidence to the 
contrary is that given by Regnault in his paper, "De la Chaleur Speciflque." We 
know that his conclusions at low temperatures are incorrect, and I do not see that 
those at higher temperatures have greater value, for his methods of observation and 
experiment were, in this case, unaltered. 

The matter, of course, can only be cleared up by a direct determination of the 
capacity for heat of water over the range 0° to 100°. 

In the meantime I contend that the evidence in favour of the formula " total 
heat = 59673 + "3990 (9 " is stronger than that upon which either Regnault's or 
Wineielmann's formula? are based. 

At temperatures above 100° the values of "the total heat" deduced by formula 
(G 2 ) would be higher than Regnault's experimental numbers. The capacity for heat 
of water at higher temperatures is so uncertain, and it has so great an influence on 
the values of L at high temperatures when deduced from the " total heat " formulas, 
that I do not feel that a discussion on these results would at present be of any value. 

The results of the experimental work described in preceding sections, and of the 
evidence brought forward in this section, may be summarised as follows : — 

The values obtained by Dietebici at 0°, by Regnault at temperatures 63 c 
to 100° C, and by Griffiths at intermediate temperatures are (assuming the 

APPROXIMATE EQUALITY OF THE " MEAN THERMAL UNIT " AND THE THERMAL UNIT AT 
15° C.) CLOSELY REPRESENTED BY THE FORMULA 

L = 596-73 - 0-60100. 

[Note, May 7, 1895. — The suggestion that the "mean thermal unit" does not 
exceed the "thermal unit at 15° C." has been criticized as over bold. It is, therefore, 
with peculiar pleasure that I include in this paper a communication which I have 
to-day received from Dr. Joly, to whom I return my sincere thanks for his permission 
to publish it. 

Dr. Joly informs me that he regards his experiments as preliminary ; their 
importance, however, is undoubtedly great. They are (I believe) the first experi- 
ments since those of Regnault which throw any light on the relative values of the 
two units. It will be seen that (assuming Bartoli and Stracciati's conclusions as 
to the changes in the capacity for heat of water from 0° to 15° C.) the results of 
Dr. Joly's experiments indicate that the ratio 

ice in terms of the same unit, by means of the ordinarily accepted comparison of the values of their 
respective thermal units, their difference becomes excessive. 
MDCCCXCV. — A. 2 T 



322 MR. E. H. GRIFFITHS ON THE LATENT 

Mean thermal unit _ 9952 __ Q-9957 
Thermal unit at 15° C. — 9995 — 1 

. . - 1-011 

in place of — - — • 

It is apparent that there is sufficient evidence to justify scepticism as to the 
validity of the commonly accepted ratio, and I hope that the demonstration of this 
uncertainty may quicken further investigation into the actual value of this important 
constant. 

Note (by Dr. J. Joly, F.R.S.) on the Ratio of the Latent Heat of Steam to the 

Specific Heat of Water. 

Upon receiving from Mr. Griffiths a copy of the abstract of his paper on the 
latent heat of steam, I determined upon making some experiments with the steam 
calorimeter on the ratio of the latent heat of steam to the mean specific heat of 
water over the range air temperature 12° to 100°. Pending the completion of a form 
of the calorimeter which will enable me to make this comparison over suitable and 
definite ranges of temperature, J gladly add, at Mr. Griffiths' request, the following 
note on the experiments already made. 

The weight of water operated upon was 12'8545 grms. This was enclosed in a 
thin blown glass bulb, sealed while the water was boiling, and having an internal 
volume of 15 "7 14 cub. centims. Ten experiments were made — these were in close 
agreement. The mean initial temperature was 11 0, 89 ; the mean steam temperature 
99 0- 96. The first temperature was determined by a Kew-corrected thermometer 
reading tenths on an open scale ; the second temperature determined by a standard 
barometer. The mean weight of steam condensed was 2'32917 grms. 

To correct this for the effect of the glass vessel, six experiments were made on the 
latter when containing dry air only. Further corrections were made (a) for evapo- 
ration within the vessel when containing water ; (b) for buoyancy or displacement 
effect on the apparent weight of the vessel, the densities being not quite the same in 
the experiments on the filled and empty vessel ; (c) for the specific heat of the air 
contained in the vessel when empty of water. A total subtractive correction of 
0'2298 grm. was obtained. 

If we now calculate the mean specific heat of water between 11 0, 89 and 99°'96, 
assuming the value of the latent heat of steam given by Mr. Griffiths' formula, i.e., 
L = 59673 — -6010 6, where 6 has the value 99°-96, we get 

_ 2 -0994 x 536-6 6 _ 
° ~ 12-8545 x 8807 ~ U ^ 

I have little doubt that this will remain — closely — the mean specific heat, 12°-100°, 
according to the steam calorimeter. It will, of course, be necessary to check the 
result by further experiments. It is true I formerly made experiments in the steam 



HEAT OF EVAPORATION OF WATER. 323 

calorimeter and obtained a higher value, but it was in an early and very defective 
form of the instrument, and an error of positive sign, as I afterwards found, very 
certainly obtained in those experiments. 

Considering this number in the light of Mr. Griffiths' remarks, it certainly 
supports his contention that Regnault made an error of excess in his value of the 
mean calorie — 0° to 100°. The above number is however, even less than the value 
supposed by Mr. Griffiths to be the true number. For, as I understand, 
Mr. Griffiths' L is calculated on the calorie at 15° C as unity. If this is also 
— as Mr. Griffiths suggests as probable — in close agreement with the mean calorie, 
0° to 100°, then the mean specific heat from 12 to 100 should come out only a very 
little less than unity. In fact, by plotting Bartoli and Stracciati's observations 
below 15°, we can estimate what the mean specific heat from 12° to 100° ought to be 
if the mean from to 100 is the same as the specific heat at 15° and both equal 
unity. A rough estimate gives this to be - 9995. 

My value is therefore too low to be in harmony with the supposition that the mean 
calorie and the 15° unit are identical. The value of the latent heat of steam is, of 
course, involved, for the steam calorimeter can only give a ratio, and, if the number 
now obtained is correct, it follows that either the latent heat assumed is too low, or 
the specific heat of water is even lower than it is supposed to be, or possibly both are 
somewhat incorrect. 

J. JOLY. 

Physical Laboratory, 

Trinity College, Dublin.] 

Section XII. — The Density and Specific Volume of Saturated Water- 
vapour DEDUCED BY MEANS OF THE THERMODYNAMIC EQUATION FROM 

the Values of L given by Formula (G a ). 

Winkelmann (as previously stated) assigns to what he terms the " theoretical 
density " of water-vapour the value 0'6225 (air = 1). He gives, however, no informa- 
tion regarding the data for this statement. 

The most recent investigation of the comparative volumes in which oxygen and 
hydrogen combine is that by Scott, whose conclusions are as follows :* " That 
100,000 volumes of oxygen unite with 200,245 volumes of hydrogen to form water. 
Applying this to the density of oxygen found by Lord Rayleigh to be 15 "8 82, we 
get for the atomic weight of oxygen 15 , 862." 

In close agreement with this conclusion we have — 

Dittmar 15-866 

Cooke and Pochards 15 - 8 6 9 

* ' Phil. Trans.,' A, 1893, p. 567. Also ' Science Progress,' August, 1S94. 

2 T 2 



324 MR. E. H. GRIFFITHS ON THE LATENT 

Assuming Scott and Rayleigh's values we get — 

Molecular weight of water-vapour = 17'862. 

Lord Rayleigh in 1888-9* pointed out that Regnault's conclusions as to the 
weights of unit volumes of hydrogen and air required correction, as Regnault had 
not allowed for the change in volume of the bulb consequent on changes in pressure. 
Crafts! has applied this correction, and finds the resulting comparative densities of 
air and hydi-ogen to be as follows : — 



Aii- 

Hydrogen .... 


Regnault's valae. 


Corrected value. 


1 
•06927 


1 

•06949 (p. 1664, ibid.) 



OstwaldJ deduces from these numbers the weights of 1 litre at 0° and 76 
centims., as 

Air, 1-29349 grams. Hydrogen, '08988 gram. 

Hence we get 

" Theoretical Density " of water-vapour = '6206 (air =1). 

I will now proceed to deduce the density at various temperatures by means of the 
thermodynamic equation 

t T / ' \ d P 

and I assume the values of the various quantities to be as follows : — 

J = 4*199 X 10 7 . (My value after Schuster's correction for the specific heat 

of the displaced air, see p. 314, supra). 

L = 59673 — '6010 6 . . . formula G 1 (supra). 

T = 273-7 + 6. 

The values of dpjdT are taken from Broch's reduction of Regnault's experimental 
results, § and are as follows : — 



* ' Proc. Roy. Soc.,' vols. 43 and 45. 

t ' Comptes Rendus,' vol. 106, pp. 1662-4, 1888. 

J 2nd ed., vol. 1, p. 181. 

§ ' Trav. et Mem. dn Bur. Intern, des Poids et Mes.,' 1, A, 1881. 



HEAT OF EVAPORATION OF WATER. 



325 



Table XVIII. 



I. 


II. 


III. 


IV. 


e. 


-^(millim. of Hg). 


-^ (dynes persq.centim.). 


p (millim. of Hg). 


o 




•330 


4401-1 


4-569 


20 


1-073 


14308 


17-363 


40 


2-936 


39150 


54-865 


60 


6-922 


92301 


148-89 


80 


14-388 


191850 


354-87 


100 


26-981 


359800 


760- 



The numbers in Column III. are obtained by assuming g = 980"94 and density of 

mercury = 13 '5 9 6. 

The resulting values of s (specific volume) and d (density, air = 1) are given in the 

following table : — 

Table XIX. 



1 

I. 


II. 


HI. 


IV. 


Temperature. 


s . 


Specific volume of air. 


d. 







207970 


128600 


•6184 


20 


58430 


36318 


■6215 


40 


19581 


12278 


■6270 


60 


7644 


4814 


•6298 


80 


3395-6 


2141 


•6305 


100 


1676-9 


1056-2 


■6299 



The specific volume of air was calculated by the formula 

1 (273-0 + 6) 760 273-0 + 

•0012935 X 273-0 X p ~ wi ^ * X " p 

The value of dp/dT at low temperatures is not known with sufficient precision to 
enable us to attach any weight to the resulting values of d. For example, if we take 
dp/dT = '331 millim. at 0° instead of "330 millim., we get d = '6204 in place of 
•6184. At temperatures above 20° or 30°, not only is the value of dp/dT known with 
greater certainty, but the effect of any small error is diminished. 

A comparison of the " Theoretical Density " (-6206) with the numbers in Column IV. 
of the last table, indicates that aqueous vapour at low pressures approximates in 
density to that of a perfect gas, but that, at higher pressures, its density exceeds that 
of a perfect gas. 

Above a pressure of about 140 millims., it appears to attain a practically constant 
density about TO 15 times that of the " theoretical " one. 



326 



MR. E. H. GRIFFITHS ON THE LATENT 



I have previously pointed out that the values of L given by my experiments are 
independent of errors in the electrical standards used during my determination of J. 
This, however, is not the case when the density is obtained from the thermo-dynamic 
equation, as the results then depend upon the absolute value assigned to the 
mechanical equivalent. Now my corrected value of J exceeds Professor Schuster 
and Mr. Gannon's by about 1 in 1000, hence the values of d in Col. IV., Table XIX., 
would, according to Schuster, have to be increased by "0006, whereas if we use 
Rowland's value (4-190) the increase would be about "0012. 

I have given the above determination of the relative densities of water-vapour and 
air, because it was the method of calculation adopted by Winkelmann, and therefore 
enables a comparison to be made between his conclusions and those arrived at by the 
use of formula G x [supra). It appears to me to be an unsatisfactory method, as it 
involves unnecessary data regarding air. A more direct way of obtaining some 
information concerning the density of water- vapour, is that of finding PV, i.e., the 
"volume energy." Now PV = BT, and the value of R for a true gas is 0-0815,* 
when P is pressure in atmospheres, and V the volume in litres occupied by the 
molecular weight in grams. Assuming as before the molecular weight of water to be 
17-862, and obtaining the values of V and P from Col. II., Table XIX., and Col. IV., 
Table XVIII., we get :— 



Temperature. 


~rjT~ = R- 





20 
40 
60 
80 
100 


■0827"] 

•0823 

■0816 

•0812 

•0811 

•0812 


as compared with 

> '0826 in the case 

of hydrogen. 



and here again we find that at temperatures near 0° water-vapour resembles a 
true gas. 



* This value of R depends on the assumptions that 1 litre of hydrogen at 0° and 76 centims. weighs 
0'08988 grain, (supra), and that the coefficient of expansion of hydrogen = '0036613 (the value 
obtained by Caldendae and myself in 1893). Dr. Shields, however, assigns to R the value O'OSIQ 
(see ' Science Progress,' December, 1894). 



HEAT OF EVAPORATION OF WATER. 327 

Appendix I. — Details oe Stirring Experiments when the Calorimeter 

WAS FILLED WITH OlL. 

The tank temperature having become steady (at # ), the calorimeter was raised to 
a temperature 1} slightly below d . In order that the conditions should become 
steady, the stirring was allowed to proceed for half-an-hour to one hour, before 
observations were commenced. The battery key (h 5 , Plate 6, fig. 2) was kept 
continually oscillating and, as the temperature rose, the swings of the galvanometer 
diminished, until no motion was observed on reversing the battery circuit. The 
observer then pressed a key communicating with the chronograph, and thus the time 
was recorded. As before stated, the stirrer automatically registered its own revo- 
lutions. At the same moment that the observer at the galvanometer pressed his 
recording key,* a second observer took the readings on the mercury thermometer, 
which gave the temperature of the steel walls. 

As any change in the mercury thermometer was of great importance, this observa- 
tion was made with the micrometer eye-piece before referred to. 

Groups of five observations were taken about certain previously fixed bridge-wire 
readings, and each group of five was meaned to find the time of passing the given 
points. 

The following Table gives full particulars of a stirring experiment. It is by no 
means a good one, but I give it simply because it is the first one done after the 
introduction of the oil. The exterior temperature was unusually unsteady. 



* In the slower experiments, however, instead of using the chronograph, I called the transit, and nay 
assistant recorded the time, as also the time of the revolutions, the stirrer ringing a bell at each 1000. 



328 



MR. E. H. GRIFFITHS ON THE LATENT 



Table XX. — Stirring experiment No. L, September 17. Temperature of 



bridge- wire = 64°'2 F. 



Bridge-wire reading. 


Time of transit. 


Reading 
thermometer II. 


No. of 
revolutions. 


Time of 
revolutions. 


589-8 
590-2 
590-6 
5910 
591-4 


P.M. 

9 45 16 
9 48 48 
9 52 58 
9 56 58 

9 59 49 


millims. 
882-40 
882-40 
882-42 
882-42 
882-40 




4000 

9000 
14000 

27000 

39000 

42000 
45000 


9 47 36 
10 12 

10 15 55 

10 31 39 

11 12 30 

11 50 15 

11 59 42 

12 9 9 


Means . 


590-8 


9 52 46 


882-41 


594-2 
594-6 
595-0 
595-4 
595-8 


10 20 11 
10 24 39 
10 28 34 
10 32 20 
10 36 36 


882-41 
882-40 
882-41 
882-48 
882-45 


Means 


595-0 


10 28 40 


882-43 


598-7 
599-1 
599-5 
599-9 
600-3 


11 3 30 
11 6 58 
11 11 
11 14 4 
11 18 30 


882-46 
882-42 
882 40 
882-40 
882-40 


Means 


599-5 


11 10 48 


882-42 


602-9 
603-3 
603-7 
604-1 
604-5 


11 48 28 
11 51 52 

11 56 54 

12 1 44 
12 6 12 


882-38 
882-38 
882-38 
882-39 
882-40 


Means 


603-7 


11 57 2 


882-39 


Mean time pe 
Hence, rate p 


r 1000 = 188-73 
er 1 sec. = 5-299 



882-41, No. II., = 40°-143 C, and 1 millim. of No. II. at 882 = -0501° C. 

1 millim. of bridge-wire (temperature 15°) at 40°*1 = "OOQIOI C, therefore, 
1 millim. of No. II. = 5'51 millims. of bridge-wire. 

The times of transit may appear, and no doubt are, very irregular. It must be 
remembered, however, that the rise in temperature between the individual observa- 
tions in each group was not so much as 0°'004 C. As this rise took about four 
minutes, it is evident that the time of transit of so slow a movement cannot be accu- 



HEAT OF EVAPORATION OF WATER. 



329 



rately determined, but observational errors of this kind are precisely those where a 
close approximation is secured by taking the mean of a group. If the middle observa- 
tion of each group is compared with the mean, it is evident that an individual 
observation might be in error by as much as 20 seconds (the greatest difference in the 
above table is 12 seconds), but it is improbable that the mean is in error by more than 
5 seconds. The example given is the one which had the slowest rate of rise, and hence 
the discrepancies are more marked than would otherwise be the case. As the total 
time of the experiment was about 2 hours 20 minutes, an error of even 10 seconds in 
the mean of each group would affect the result by but 1 in 800, and as an error of 
1 in 50 in the value of Q,, would only affect my final values of L by 1 in 5000, the 
above order of accuracy was moi - e than sufficient. 

I will now give the reduction of the observation in the above table. 

Reduction of Stirring Experiment No. I. 



Bridge- wire 
range. 


Time 


Change in 
thermo- 
meter II. 


Resulting 

change 

in range. 


de x 

dt 


Correction to 

mean 
bridge- wire. 


Correction 

for 
temperature 
bridge-wire. 


de x 

dt 
corrected. 


A 
B 
C 


590-6-595-0 
595-0-599-5 
599-5-603-7 


2154 
2528 
2772 


+ •02 

-•014 

-•030 


+ ■11 
-•07 
-•17 


•002094 
•001753 
•001454 


- 04 
-1-2 
+4-3 


+ 1-7 
+ T5 
+ 1-2 


•002090 
•001753 
•001460 



Since A, B, and C should, if the exterior temperature (No. II.) had not changed, 
fall on a straight line, the most probable path is obtained by taking -g- (2A + B) and 
J (B -f- 2C) as the rate of rise at the corresponding bridge-wire readings, hence 
Ave get 



Bridge-wire. 


dOjdt. 


594-28 
600-15 


•001978 
■001558 



Now the bridge-wire null-point = 598"35 + ■O30 1 (see p. 288). Therefore null- 
point at 40° = 599"55. We can now deduce the value of dOJdt at this null-point. 
We get -001600. 

Hence 

(dejdt),— -001600, 

when r 1 = 5 -2 9 9 and 1 is measured in millims. of the bridge- wire scale. 

I think that there is no necessity to give details of the remaining experiments ; 
mdcccxcv. — a. 2 u 



330 



MR. E. H, GRIFFITHS ON THE LATENT 



the following table shows the results of all those experiments at different rates 
where O = 40°'l approximately. 

Table XXI. 



Experiment. 


Date. 


(de{\ 

\ dt )>• 


r. 


Let t = time of rising- 1 millim. of bridge-wire, then 


tr 
X 10" 1 . 


tr* 
X lO- 2 . 


tr s 

XlO- 3 . 


tr 4 - 
X lO- 3 . 


From formula 

A. 

(infra) . 


I. 

IX. 

VI. 

II. 

III. 


Sept. 17 
Oct. 27 

„ 7 
Sept. 23 

„ 24 


■001600 
•001626 
•001793 
■002152 
•008] 52 


5-299 
5-310 
5-456 
5-670 
7-899 


331 

327 

304 

263 

97 


176 
173 
166 
149 
76 


930 
921 
906 

847 
605 


492 

489 
494 
480 
478 


•001606 
■001619 
•001805 
•002104 
•007930 



Experiments II. and III. were only performed with the object of ascertaining the 
effect of changes of rate. Although the differences between ti A may appear consider- 
able, it must be remembered that this constant was only required in order to reduce 
experiments at different rates to some standard rate ; in reality, when we consider 
that we are dealing with the fourth power of r the uniformity is remarkable. 

If we plot the values of (d0i/dt) s obtained from the formula 



dt 



491000 



(A), 



the results are in close agreement with the experimental ones, especially when the rate is 
between 5 "2 and 5 "5 (the extreme limits of rate during the Latent Heat experiments, 
the usual value being about 5 '3). True, if we assume (dd-Jdt) s =■ r 3 /92000 our results 
would be nearly as close over the above limited range, but Experiments II. and HI. 
indicate that the true relation is more nearly given by the previous expression. In 
any case, the difference between the experiments and the results as deduced from 
(A) do not differ by 1 in 100 over the above range of rate, and a difference of 1 in 
100 in Q^ would only cause a difference of about 1 in 10,000 in L. 



Table XXII. — The experiments at 30° give the following results. 



Experiment. 


Date. 


(de x \ 
\ dt A- 


r. 


tr 5 x 10-2. 


tr 1 X lO- 3 . 


From formula 

B 

(infra). 


IV. 

VIII. 

VII. 

V. 


Sept. 29 
Oct. 27 

,. 7 
7 


•002330 
•002380 
•002568 
•005973 


5-280 
5-320 
5-416 

6-750 


629 
632 
619 

515 

1 


333 
337 
335 

348 


•002314 
•002383 
•002560 
•006178 



If we assume 



we get 



HEAT OF EVAPORATION OF WATER. 



ti* = 336000, 



331 



dt Js 



(B). 



And here again the differences between the experiments and the results from (B) 
are much below 1 per cent, at rates between 5*2 and 5*5, and again the experiment 
at higher speeds (Expt. V.) indicates that ti A is more constant than tr z . 

Applying formulae (A) and (B), we can deduce the rise for a rate of 5*300. 

Values of (ddjdt) s at rate 5*300 :— 



Temperature. 


(dejdt),. 


40°T 
30-0 


•001608 
•002348 



Now (see Appendix II., Experiment IV.) it was found that when a similar experiment 
was performed at 40 o, l, where the beat supply was that due to a potential difference 
of three Clark cells at 15° together with a stirring supply (at rate 5*277), then 

(ddjdt) es = "14853 (mean bridge-wire millim.). 

Now (from A) we get 



therefore 



hence 



(ddjdt), = *00158 at rate 5*277, therefore (ddjdt)^ = -14695, 



(dd 1 /dt) e =^^= -01633, 



(ddjdt), _ 161 
(ddjdt), ~ 1633 



at rate 5*300 (supra) = *0986. 



Now the corrected resistance at this temperature (Table VIII.) was 10*376 ohms 
where the D.P. was that of one Clark cell, and since 



H 



1-4342* 



therefore 



E^J P 61 ' S6C -' We haVe 10*376 x 4198 = "° 4723 therm&1 ^ &m ' 



Q, (rate 5*300) =* "04723 X '0986 = *004659 thermal gram. 

2 u 2 



332 MR. E. H. GRIFFITHS ON THE LATENT 

In the same manner (Appendix II., Experiments V. and VI.) it was found that 
at temperature 30° 

(cldjdt)^ = -15035, and (dd^di), = "002348 (formula B, supra), 
hence 



and at 30 

therefore 

therefore 



o 



W4 _ 234^8 _ 
(d6Jdt) e ~ 1671 ~~ ' 

Ej = 10-348, 



1-4342 2 
H = -, A ; n — TTTT^; = "04735 thermal gram per sec. 
10-348 x 4-198 ° r 



Q, (rate 5-300) = "04735 X '1405 = -006654 thermal gram. 



Now assuming (A) and (B), it follows that r 4 /Q s is constant, and we can deduce 
that if 1\ be any rate and 5 '300 the standard rate 

At temp. 40°-l, Q,= -004659 + (r! 4 - 789) X -0000059 .... (C). 
At temp. 30°-0, Q, = "006654 + (r± — 789) X "0000084 .... (D). 

I performed one stirring experiment at 50° and two at 20° and I give the results 
only, as the values of Q s at these temperatures are not required for the reduction of 
the L experiments described in this papei*. I was unable (for want of time) to prove 
how nearly the effect of changes of rate could be expi'essed in the same manner as at 
30° and 40°, but as the rate was nearly 5 "3, the corrections introduced by the reduction 
to rate 5 "3 were very small. The results were of use, as on plotting the curve for 
the values of Q s at the four different temperatures it showed no signs of irregularity, 
and thus gave additional strength to the determinations at 30° and 40°. The values 
are as follows : — 

At temp. 50°, Q, = '00235 + (r* — 789) X '0000030 .... (E). 

At temp. 20°, Q, = "00768 + (rf — 789) X "0000098 .... (F). 

The values of Q* at 30° and 40° receive a certain amount of support from the 
preliminary experiments referred to in Section VII. Although my results by that 
method varied considerably amongst themselves, the mean of five experiments at 40° 
gave "00000802 gram of water evaporated per 1 sec. by the stirring after reduction 
to rate 5*3, and the mean of four experiments at .30° gave -00001137 gram of H 3 
evaporated per sec. at the same rate. 



HEAT OF EVAPORATION OP WATER. 333 

Now, if we assume L at 40° = 573 and L at 30° = 579, we can deduce the values 
of Q s , which are as follows : — 

At 40°, Q, = -00460 
„ 30°, Q s = -00658. 

These results differ from those obtained without any weighing or passing of air 
(equations C and D supra) by 1 in 77 and 1 in 94 respectively. As an order of 
accuracy of 1 in 50 was sufficient for my purpose, T considered this independent 
evidence valuable, although I believe the former method to be by far the most exact. 

I also performed a determination of Q., at 50° by an evaporating experiment. This 
gave -00000521 gram per sec, Assuming L = 567, this would give Q, = '00295, 
far too high a value as compared with that given by equation (E). This evaporation 
experiment was a very unsatisfactory one, however, and I attach but little importance 
to it — in any case, the doubt would not affect the values of L. 

To conclude this portion of the subject, I admit that it would have been advisable 
to perform more of these stirring experiments at 30° and 40°, but at the same time, 
I think the evidence is sufficient to warrant the assumption that the values of Q s 
cannot be in error by as much as 1 in 50 and are probably correct to better than 
1 in 100. 



Appendix II. — Details of the Experiments by which the Capacity for 
Heat of the Calorimeter and Contents was ascertained. 

The temperature of the calorimeter was adjusted in the same manner as that 
described in Appendix I. 

The time of transit across five bridge-wire divisions about the readings 50, 60, and 
70 centims. was taken, and the times at 50, 60, and 70 deduced. I give particulars 
of Experiment IV., as that was the one quoted in Appendix I., from which the 
value of Q s at 40 - l was deduced. 



334 



MR. E. H. GRIFFITHS ON THE LATENT 



Table XXIII.— Experiment No. IV., September 17. 

Number of Clai-k cells 3 (each consisting of 4 in ll 1 ). Temperature cells, 15 0, 14 C. ; 

temperature bridge- wire, 63°'5 Fahr. 



Bridge-wire reading. 


Time 
(chronograph) . 


Revolutions 
(1000's). 


Time. 


External temperature 
by thermometer II. 


49 

49-5 

50 

50-5 

51 

59 

59-5 

60 

60-5 

61 

69 

69-5 

70 

70-5 

71 


81-7 
1136 

144-6 
176-9 
207-5 




3 
4 

7 
Time per 1000 


100-1 

669-0 
858-5 

1426-6 


882-35 
882-39 


144-9 


882-37 


730-5 
764-1 
797-6 
8314 
865-6 


882-40 
882-40 


797-8 


882-40 


14210 
1456-6 
1493-3 
1529-0 
1565-7 


882-40 
882-40 


14931 


189-50 
.-.r 1 = 5-277 


882-40 







The operations necessary for the reduction of Experiment IV.'" are as follows : — 

Data required. 

Mean value of 1 centim. of range in terms of mean bridge-wire centim. (given by 
calibration of bridge- wire ; see p. 285) — 

50 to 60 1-00082 

60 to 70 . . . . . . . -99551. 

Correction for temperature bridge-wire to 15° C. = range {1 + -00016 (F.° — 59)} 
* Fuller particulars concerning this method of reduction will be found in Paper A. 



HEAT OF EVAPORATION OP WATER. 



335 



1 rnillim. of No. II. = 5"51 millims. of bridge-wire, and 882"40 rnillirns. = 40°"142. 
Bridge-wire null-point = 599"55 millims. 



Range. 


Time 

over 

range. 


Change 

temperature 

on therm. 

II. 


Resul ting- 
change 
range. 


de^dt xio 4 . 


Correction to 

mean 
bridge-wire. 

X10*. 


Correction for 

temperature 

C. cells and 

bridge-wire 

xlO*. 


Corrected 

de^dt 

xl0±. 


centims. 

50 to 60 
60 to 70 


652-9 
695-3 


+ •03 +T6 



15339 
1438T 


+ 1-3 

-6-4 


+ •4, +1-1 
+ ■3, +10 


1536-7 
14330 



Hence we get "15367 and "14330 as the values of (ddjclt)^ at 55 and 65 centims. 
respectively. We can thus deduce the value at the null-point (5 99 "5 5). We get 
•14853. 

Now (Appendix I.) the value of (dOJdt),, for rate 5"277 = "00158, therefore 
(d0Jdt) 3e = "14695. 

I rift v P y C* 

Now ( -r 1 ) x gives the rise per second in degrees C. with unit resistance 

and unit potential difference, where R 1 is the resistance in true ohms of the coil at 
temperature 6 V n the number of Clark cells of P.D. e volts, and Cj the value of the 
mean bridge-wire milium at 15° C. when 8 l = 40°'l, expressed in terms of the N 
thermometer (see p. 289). Hence if T is the time of rising 1° C, we get 



T = 



(ne) 2 



(ddjclt), x E, x C f 



and 

therefore 
and 

therefore 



R 38 = 10-377 (see Table VIII.), (nef — 18-513, and C 4 = "009100, 

T = 1334"1, 



T 
C 8l = - (where C B[ is capacity for heat at 6{), and J = 4 - 199, 



C e = 317'82 thermal grams. 



The following table gives the results of all the experiments made with the object of 
obtaining the values of C 9l . 



336 



MR. E. H. GRIFFITHS ON THE LATENT 



to 
-p 

a 

<D 

a 
o 

O 

•n 

a 

u 

CD 

■8 



o 
13 
Q 

O 

ce 

CD 

w 

- — 

o 

cS 

Oh 

OS 

o 

cd 



O 



3 



CD 

CD 



X 
X 

H 





■4- 


+- 




-3- 








CO 


-* 


-3< 


CO 


r^ 


•—< 


to 


o 


o 


1^ 


t>- 


CO 


CO 


-* 


co 


to 


II 


^# 


OJ 


r~ 


-* 


CM 


CM 


!>• 


CM 


l-H 


|-H 


r—\ 


rH 


i— 1 


o 


En H 


CO 


CO 


CO 


CO 


CO 


CO 


CO 




-a 

o 


















X 
















11% 


.—1 

P3 


00 


rH 


rH 


en 


in 


l—i 


o 


CO 


CM 


■* 


rH 


•—* 


rH 


i-H 


EH s 


X 


co 


*S 


CO 


CM 


i—< 


i — 1 


OS 


CO . 


CO 


CO 


CO 


CO 


CO 


CM 




eo 


1—1 


1— 1 


rH 


1— 1 


•—t 


rH 


r—^ 




$!i 
















CO* 

»© 


00 


o 


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=3 A -M 








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HEAT OF EVAPORATION OF WATER. 337 

In Paper A. I have given a full account of the determination of the " water 
equivalent " (Wj) of this calorimeter, and I have every confidence in the values there 
given 

From Table VI. of that Paper I extract the following : — 

$ 1 W v 



20 


80-11 


30 


80-90 


40 


82-19 


50 


83-39 



During these experiments, the silver flask contained a mercury thermometer (Go) 
which was used, during my earlier L experiments, to indicate the internal temperature 
of the flask. As described (ante), a metal conical tube had been cast on to the stem 
of this thermometer by means of the alloy, and the tube carefully ground into the 
neck of the flask to prevent any diffusion of vapour up the glass tube, down which 
the thermometer passed. After I adopted the " exhaust " method of performing the 
L experiments, this thermometer was removed from the apparatus ; this occurred 
between Experiments III. and IV., Table XXIV. I had forgotten the circumstance, and 
when I reduced the results, I was much troubled as to the different values of C 9i given 
by Experiments II. and IV., which were at about the same temperatui'e. It was some 
time before the cause of the discrepancy suggested itself to me. I then obtained an 
approximation to the capacity for heat of thermometer G 3 and tube, as follows : The 
temperature of both calorimeter and tank being steady, the bridge was adjusted until 
the galvanometer ceased to swing. Thermometer G 2 was then suspended above the 
tube communicating with the flask, and its temperature read by the reading micro- 
scope. It was then rapidly lowei'ed into its place, and observed until its temperature 
became steady (this took place in about 4 to 5 minutes). The tank being at 40° and 
the external temperature about 20°, the thermometer rise was about 20°, and a small 
error in reading was of little consequence. The bridge contact-maker was then 
re-adjusted, and the change in temperature of the calorimeter deduced from the 
difference in the readings. Hence the capacity for heat of G 2 could be found. Four 
experiments were performed with the following results : — 



(1) 


1-52 


(2) 


1-65 


(3) 


1-62 


(4) 


1-58 


• • 


159 



Mean 



mdcccxcv, — a. 2 x 



338 



MR. E. H. GRIFFITHS ON THE LATENT 



If we assume the capacity as 1"6, we cannot be greatly in error, and this quantity 
must be subtracted from the values of W x (supra) for all experiments after No. 3. 
Now the values of C 9i from Experiments II. and IV. differ by 1*89. This apparent 
difference of *3 in the results has, however, to be further diminished. On September 14, 
I found it necessary to withdraw thermometer AB from the calorimeter. Before 
doing so, I weighed a " weighing bottle " containing a roll of blotting-paper, and on 
removing the thermometer, I wiped its stem and bulb with this paper in order to find 
the weight of oil withdrawn, which proved to be '104 gram. Hence the differences 
in Column VI. of the next Table. 



Table XXV— Specific Heat of Oil. 



I. 

Experiment. 


II. 
Tempera- 
ture. 


III. 

Ca, (Table 
XXIV.). 


IV. 

Wi (supra). 


V. 

Cap. of oil. 


VI. 

Wt. of oil 

(vacuo). 


VII. 

s v 


III. 

II. 

IV. 

I. 

V. 

VI. 

VII. 


o 

50-024 
40-122 
40-142 
31-996 
29-979 
29-998 
20-031 


324-74 
319-74 
317-88 
314-87 
31241 
31235 
307-50 


83-39 

82-20 

80-60* 

81-14 

79-30* 

79-30* 

78-51* 

! 


241-35 

237-54 
237-28 
23373 
233-11 
233-05 
228-99 


474-12 

474-12 

474-02f 

474-12 

474-02f 

474-02-j- 

474-02f 


•5090 
•5008 1 
•5005 / 
•4930 
•4917 \ 
•4916 / 
•4830 



Appendix III. — Details of Determination of K x . 

In Paper J., p. 409, is given a table showing the errors of all the individual coils in 
my dial resistance box. These errors were, by kind permission of Mr. Glazebrook, 
ascertained by direct comparison with the B.A. standards. 

I extract the following from the remarks on that table (p. 410, ibid.) : 
" A table was constructed giving the total difference between the reading and the 
real value (in terms of " legal ohms ") for every position of the plugs in each dial. 
This difference we termed the "plug correction."! Having made this correction, we 
had then to correct for any inaccuracy in the ratio arms of the bridge, and as all 
determinations of the calorimeter coil resistance were made with 1000 (right) and 
10 (left) as the arms, it is only necessary to here give the correction for those coils. 



"Now 



10L/1000R = 9-9977/1000-30 = 0'0099947. 



* After removal of thermometer Gr 9 . 
f After removal of -10 gram oil. 

% The correction for the temperature of the coik was made before applying the "plug correction." 
§ There is here a mistake in Paper J. This was corrected in a subsequent communication, ' Proc. 
Roy. Soc.,' vol. 55, p. 25. 



HEAT OF EVAPORATION OF WATER. 



339 



" This we termed the " bridge correction." 

" The resulting values are expressed in legal ohms, and true ohms = reading in legal 
ohms (1 - -0024275)." 

The above extract is sufficient to explain the operations. I now give a complete 
example of a determination of R x and the subsequent calculations. 

The value of O we obtained by dii-ect observation of thermometer II., and d' by 
observation of the bridge reading. Then 8 l = 8 -\- d'. 



Table XXVI. — Determination of Coil Resistance. October 11. 



See p. 296. 


Galvanometer 

swings.* 


Observed 
R. 


Tempera- 
ture coils. 


R + r. 


Correction 
for tem- 
perature 
coils. 


Plug- 
correction. 


R + r 
(box ohms). 




331 170 














*i 


191 341 
140 171 

417 296 


5sm 




58-450 


+ •002 


+ ■007 


58-459 


N 3 


222 350 
195 54 

407 281 


1095H| 


17°-08 


1095-783 


+ ■033 


+ •777 


1096-583 


N 3 


201 322 
206 41 

282 128 


1095fff 




1095-834 


+ •033 


+ •777 


1096-634 


»4 


173 329 

109 201 


58ifi^ 


* ' 


58-352 


+ •002 


+ •007 


58-361 



As previously remarked, the difference in the resistance of the leads accounts for 
the difference between N 3 and N 3 , and Nj and N 4 . 
We thus get 

Rj + r, = { (N 2 + N 3 ) - (Nj + NJ } / 2 = 10*38199 box ohms. 

= 10-37648 "legal" ohms. 
= 10-35128 true ohms. 

Reading of thermometer No. II. = 68477 minims. = 29°-997 C. 

„ bridge- wire — 590'1, and null-point = 599-25 (see p. 288). 



Therefore 



d' = - -084° C. 



* Resistance in battery circuit (2 Leclanchcs) = 700 ohms when observing N 2 and N 3 , and 2900 ohms 
when observing Nj and N 4 . 

2X2 



340 MB. E. H. GRIFFITHS ON THE LATENT 

Hence 6-y — 29 0, 913 and R : + r — 10-3513 true ohms, 

therefore, when 6 l = 30°'000 Rj + r = 10-3515 „ 

The values of E. x + r at about 30° were also ascertained on other dates, and were 
as follows : — 



Date. 


Temperature. 


Rj + r. 


f^ + r at 30°. 


,,io 

., 11 


o 

30-003 
30-245 
30-044 
29-913 


103516 
10-3522 
10-3518 
103513 


10-3516 
103516 
10-3517 
103515 



I think it unnecessary to multiply examples at other temperatures, the above will 
show the order of accuracy. 

From the above values, the value of r ( = "0034, see p. 296) must be subtracted in 
each case to get the value R u given in Table VIII., p. 297. 



Description of Plates 4, 5, and 6. 



PLATE 4. 



The lower figure is a vertical section of the steel chamber and tank. The spaces 
filled with mercury are printed in black. The tube at I) communicated 
with the regulating apparatus. 

The upper figure is a plan of the lid. 

PLATE 5. 

Fig. 1 is a vertical section of the calorimeter. When gas was driven through the 
apparatus it entered atyj passed into the bottom of the silver flask F at G 
and left it near the roof at d. It descended to the bottom of the 18 ft. 
silver coil (sections of which are shown by the small circles at C 3 ), then 
ascended a gentle slope and finally left the calorimeter by the tube e. 
Although in different planes from the section, the position of the platinum 
thermometer is indicated as well as S, the bottom of the stirrer. A " dropper " 
is shown in position in the tube h. 

Fig. 2 is a horizontal section across the calorimeter at AB in fig. 1. 

Fig. 3 is a plan of the lid. 

The stirring shaft passed through S, the platinum thermometer down T, 
and the tube ti established communication with the flask F (fig. 1). The 
ends of the silver spiral are shown at c and/! 



HEAT OF EVAPORATION OP WATER. 341 

Fig. 4 shows the method of insulating the leads where they passed through the lid of 
the calorimeter at I and V (fig. 3), and also the insulation of the four leads 
where they passed through the steel lid (see small sketch, Plate 6, fig. 3). 

PLATE 6. 

Fig. 1 is diagrammatic only, for the various tubes, &c, repeatedly crossed each other. 
The gas on entering passed through H 3 S0 4 at S, then through P 2 5 at P, 
afterwards through the 30 ft. coil indicated at C, and thus attained to the 
temperature of the tank watei*. Mj is an open scale manometer to show 
the pressure of the gas when entering the flask F. Leaving this flask near 
the top, the vapour traversed the coil G, and thus attained the temperature 
of the calorimeter ; it then passed through the four- way tap T 4 , and on 
emerging from the tank passed over a row of small gas jets, shown at G. 
The tubes between T 4 and B could be swept by dry air, by use. of the taps 
T 2 and T,,. All the apparatus within the dotted lines was immersed in the 
tank water. 

Fig. 2 shows the arrangements of the differential thermometers and the bridge. 
The coil of AB is in series with the compensators of CD and vice verm. 

Fig. 3 shows the electrical connections with the calorimeter coil. 

A coil in the tank at F was of the same resistance and wire as the 
calorimeter coil. By means of the key K 1 the current could be switched on 
to either coil. ~K V was also connected with the chronograph in such a 
manner that all its movements were recorded. 

By means of the Rheochord the external resistance of the storage circuit 
(leads 2 and 4) could be so adjusted that the D.P. at the points M and 
N was always that of the Clark cells. Wires numbered 1 and 3 are in the 
Clark cell circuit. 



VriMths. 



Phil. Trans. 1895 A. Plate 4. 




Tnat.sije. 



Griffiths. 



Phil. Trans. 1895 A. Plate 5. 



Calorimeter. 
3 Anat size. 



Section 




Ficf.3. 



n g .i. 



Griffiths. 



Phil Trans. 1895 A. Plate 6. 



JfO 0J_ 



f 










[ 343 ] 



X. Contributions to the Mathematical Theory of Evolution. — II. Skew Variation in 

Homogeneous Material. 

By Karl Pearson, University College, London. 
Communicated by Professor Henrict, F.R.S. 

Received December 19, 1894, — Read January 24, 1895. 

Plates 7-16. 

Contents. 

Part I. — Theoretical. 

Page. 

Section 1. — Classification of asymmetrical frequency curves in general. Types actually 

occurring 344 

Sections 2-5. — Fitting of point-binomials by methods of quadratic and cubic 345 

Section 6.— Illustrations in cases of barometric heights and crab measurements 351 

Section 7. — Fundamental geometrical relation between symmetrical binomial and normal 

frequency curve 355 

Section 8. — Extension of this relation to the deduction of a skew frequency cui've from 

the asymmetrical binomial 356 

Sections 9-10. — General remarks on the defects of the normal frequency curve as applied to 

actual statistics. Skewness and limited range. The five types of theoretical curves . . 357 

Section 11. — The hypergeometrical series as replacing the point-binomial. Curves related to 
the hypergeometrical series in the same manner as the normal curve to the symmetrical 
point-binomial 360 

Sections 12-13. — Equations to the possible frequency curves deduced from the hyper- 
geometrical series 362 

Section 14. — Curve of Type I. Skewness with range limited in both directions. Criterion 

for the existence of this type and method of fitting 367 

Section 15. — Special case of range being given 370 

Section 16. — Special case of one end of range being given 371 

Section 17. — Curve of Type II. Symmetrical with range limited in both directions. This 
curve better than the normal curve, if observations vary on the side of a point-binomial 
from normality 372 

Section 18-18 his. — Curve of Type III. Skewness and range limited in one direction only. 

Criterion and method of fitting 373 

Sections 19-20. — Curve of Type IV. Range unlimited in both directions, with skewness. 

Criterion and method of fitting. Discussion of the G-integral 374 

16.7.95, 



344 MR. K. PEARSON ON THE MATHEMATICAL THEORY OF EVOLUTION. 

Part II. — Practical. 

Statistical Examples. 

Page. 

Section 21. — The range of the barometer 381 

Section 22. — Crab-measurements (Weldon No. 4) 384 

Section 23. — Variation in height of recruits 3S5 

Section 24. — Variation in height of school-girls aged 8 386 

Section 25. — Variation in length-breadth index of 900 Bavarian skulls 388 

Section 26. — Frequency of enteric fever with age 390 

Section 27. — Distribution of guesses at mid-tints 392 

Section 28. — Distinction between " skewness " and " compoundness " in case of crabs' 

"foreheads" 394 

Section 29. — Frequency of divorce with duration of marriage 395 

Section 30. — Frequency of houses with given valuations 396 

Section 31. — Variation in number of petals of buttercups 399 

Section 32. — Variation in number of projecting blossoms in clover 402 

Section 33. — Variation in number of dorsal teeth on rostrum of prawn 403 

Section 34. — Variation in pauper-percentages in England and Wales 404 

Section 35. — Resolution of mortality curve for English males into components 406 

Section 36. — Concluding remarks on skewness, variation, and correlation (correlation ovals 

for whist) 410 

Note on Thiele's treatment of skew frequency 412 

Part T. — Theoretical. • 

Asymmetrical Frequency Curves. 

(1.) An asymmetrical frequency curve may arise from two quite distinct classes of 
causes. In the first place the material measured may be heterogeneous and may 
consist of a mixture of two or more homogeneous materials. Such frequency curves, 
for example, arise when we have a mixed population of two different races, a homo- 
geneous population with a sprinkling of diseased or deformed members, a curve for 
the frequency of matrimony covering more than one class of the population, or in 
economics a frequency of interest curve for securities of different types of stability — 
railways and government stocks mixed with mining and financial companies. The 
treatment of this class of frequency curves requires us to break up the original curve 
into component parts, or simple frequency curves. This branch of the subject (for 
the special case of the compound being the sum of two normal curves) has been 
treated in a paper presented to the Roj^al Society by the author, on October 18, 1893. 
The second class of frequency curves arises in the case of homogeneous material 
when the tendency to deviation on one side of the mean is unequal to the tendency 
to deviation on the other side. Such curves arise in many physical, economic and 
biological investigations, for example, in frequency curves for the height of the 
barometer, in those for prices and for rates of interest of securities of the same 
class, in mortality curves, especially the percentage of deaths to cases in all kinds of 



MR. K. PEARSON ON THE MATHEMATICAL THEORY OF EVOLUTION. 345 

fevers, in income tax and house duty returns, and in various types of anthropological 
measurements. It is this class of curves, which are dealt with in the present paper. 
The general type of this class of frequency curve will be found to vary (see Plate 7, 
fig. 1) through all phases from the form close to the negative exponential curve : 

y = Ce-*>*, 

to a form close to the normal frequency curve 

y = Ce-ps, 
where C and p are constants. 

Hence any theory which is to cover the whole series of these curves must give a 
curve capable of varying from one to another of these types, i.e., from a type in 
which the maximum* practically coincides with the extreme ordinate, to a type in 
which it coincides with the central ordinate as in the normal frequency curve. 

It is well known that the points given by the point-binomial (-| ~j- ^)" coincide very 
closely with the contour of a normal frequency curve when n is only moderately 
large. For example, the 21 points of (^ + |-) 30 lie most closely on a normal frequency 
curve, and the author has devised a probability machine, which by continually bisecting 
streams of sand or rape seed for 20 successive falls gives a good normal frequency 
curve by the heights of the resulting 21 columns. Set to any other ratio p : q of 
division other than bisection, the machine gives the binomial {p + q) 20 , or indeed any 
less power and thus a wide range of asymmetrical point-binomials. Plate 7, fig. 2, 
represents, diagramatically, a 14-power binomial machine. 

Just as the normal frequency curve may be obtained by running a continuous 
curve through the point-binomial (^ -f- ^)" when n is fairly large, so a more general 
form of the probability curve may be obtained by running a continuous curve through 
the general binomial (p + q) n . As the great and only true test of the normal curve 
is : Does it really fit observations and measurements of a symmetrical kind ? so the 
best argument for the generalised probability curve deduced in this paper is that it 
does fit, and fit surprisingly accurately observations of an asymmetrical character. 
Indeed, there are very few results which have been represented by the normal curve 
which do not better fit the generalised probability curve, — a slight degree of 
asymmetry being probably characteristic of nearly all groups of measurements. 
Before deducing the generalised probability curve, it may be well to show how any 
asymmetrical curve may be fitted with its closest point- binomial. This will be the 
topic of the following five articles. 

(2.) Consider a series of rectangles on equal base c and whose heights are respec- 
tively the successive terms of the binomial {p-\- q)" X a/c, where r p -\-q=l. Here a. is . 
clearly the area of the entire system. Choose as origin a point O distant \c from the 

* I have fonnd it convenient to use the term mode for the abscissa corresponding to the ordinate of 
maximum frequency. Thus the "mean," the "mode," and the "median " have all distinct, characters 
important to the statistician. 

MDCCOXOV. — A. 2 Y 



346 MR. K. PEARSON ON THE MATHEMATICAL THEORY OP EVOLUTION. 



boundary of the first rectangle, on the line of common bases, and let y r be the height 
of the r th rectangle, or 



l Jr — 



- JL « (» - 1) ■ ■ . (« - r + 2) +J __, 



while 



\r - 1 



Vi ~ a P n l c ■ 



p" 



•e-C-s^-C-ie-C-SK-C^*- C -*e- C-*- C-»e-C-»<- C-» 

JT 



Let us find the values of 



2{y r c X (re)*}, 



where s is any integer, for values of s from to 4. 
It is easy to see that 

2 {y r c X (re)' } = «c< | (g |) (g ^) . . . g (p + g)», 

where the operation cZ/c/g is repeated 5 times. 

The operations indicated can easily be performed by putting q = e" when 



2 {y r c X (re)*} = 






{e*(p + e*)"}, 



and the successive values can be found by Leibnitz's theorem. After differentiation 
we may put p + q or p + e" = 1. There results : 

S (y r c) — a 

2 (y t o X re) ■= ac{l A- nq] 

2 (y r G X (rcf) = ac 3 {l + 3ng + » (n - 1) </} 

2 (2/,c X (re) 3 ) = ac 3 {1 + 7^ + 6n (n — 1) g 2 + n (n - 1) (n - 2) g 3 } 

2 (y r c X (re) 4 ) = ac 4 {l + 15ng + 25n (n - 1) g 2 + lOn (n - 1) (n - 2) g 3 

+ n (n - 1) (to — 2) (n — 3) g 4 }. 

Let NG be the vertical through the centroid of the system of rectangles, then 
clearly 

ON = 2 (y r c X rc)/a = c {1 + ng}. 



MR. K. PEARSON ON" THE MATHEMATICAL THEORY OF EVOLUTION. ■ 347 

We shall now proceed to find the first four moments of the system of rectangles 
round GN. If the inertia of each rectangle might be considered as concentrated along 
its mid vertical, we should have for the s th moment round NG-, writing d = c (1 + n 'l)> 

a.fi s = 2 {ij,c X (re — d)'}. 

The resulting values are 

fi. 2 = npqc 2 

fi 3 = npq(p -q)c s 

/x i = npq {1 + 3 (n — 2) pq} c 4 , 

whence, remembering that p -f- q = 1, we find that p and q are roots of 

„% „ , (W - M 4 ) lh + /* 3 a A 

2 2 + 4 /.. 3 v — r^~i = °> 

4 {.TfJ, 2 - — fl i ) /M 2 4- (l/ig- 

M V? 3 „ _ \/i 2 (W ~ Pi) ht + W} 

Thus, when /% fi s , and ^ have been calculated for the frequency curve, the 
elements of the point-binomial are known. These results were given by me in a 
letter to 'Nature,' October 26, 1893. 

They give quite a fair solution so long as n is large and c small, i.e., so long as the 
asymmetry and the "excess : ' (' Phil. Trans.,' vol. 185, A, p. 93), measured respec- 
tively by ju 3 and /a 4 — 3/x^ (which vanish for the normal curve) are not considerable."" 
In many cases, however, they are considerable, and the following solution is perfectly 
general. 

* If y denote the largest term in (p + q) n and yi the rth term beyond it, then an application of 
Stirling's theorem — if n be large— shows that 

_ /, t v- /, . * \-«-a«- 



Take 

log u = it -pn - f) log (l -—) 

log v=(-t- cpi - |) log (l + — 
and expand the right hand side in powers of i, we find 



_ / J_\ £_r _ _l_-i _ _fi_ I _ _L_\ t* I 3 \ _ 

\ 2pn/ 2pn \ 2pn J Qp-n" \ pn / 1 2p 3 » 3 \ 2pnj 

Hence, remembering thatp + q = 1, we have 

log „. = _ Hpi) * (i - L-^e) + Zjgzjl (, _ Lzn) 

Ipqn Znpq \ znpq / b'p'q'n- \ npq j 



it I n 3(l-4>pq 4-2pV)\ 

- i2^%g(l - Spq - -±- H m Pq) ) + etc. 

Now, making use of the valnes given in § 2 for ft*, fi s , and /i, p and writing t x c = a, - , and y t = y, 
we find 

2 Y 2 



348 • MR. K. PEARSON ON THE MATHEMATICAL THEORY OF EVOLUTION. 

(3.) To find the nth. moment of a trapezium ABCD about a line parallel to its 
parallel sides, ?/j and y. 2 being the lengths of the parallel sides, x x , x 2 , their distances 
from the moment- axis, and x. z — x 1 = c. 




Ok x, 



Sx \ 



■x, 



Let M„ be the Jith moment. Then 



M„ = yx"dx 



_ ■% - V x ^ 3 * +3 ~ °\ n+2 , Vvh - Vzh ^" +1 - ; 'h" +l 



a\ — x l n + 2 



+ 



Xo — .('-, 



n + 1 



_ ,. ( x ll _ JL X -V , 1<*=2: r «-2,.3 _ n (n - 1) (,i-2) B _ 3 
~ y z\\2 [3 2 + (4 3 (5 X3 C + 



— yi 



71 

!3~ 



^ + 1 =.^V + 



14 



, n (n - 1) (« -2) 

-J i Li L T n-3 A j_ 

L 5 *2 c . 



;• 



(4.) Now consider a curve of observations made up of a series of trapezia on equal 
bases, as in the accompanying figure : 



y = y „